diff --git a/src/samples/Sample04/Activities/ArithmeticOperation.cs b/src/samples/Sample04/Activities/ArithmeticOperation.cs
index d00c3e385..24f2a7b5e 100644
--- a/src/samples/Sample04/Activities/ArithmeticOperation.cs
+++ b/src/samples/Sample04/Activities/ArithmeticOperation.cs
@@ -1,7 +1,6 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Elsa.Expressions;
-using Elsa.Extensions;
 using Elsa.Services;
 using Elsa.Results;
 using Elsa.Services.Models;
@@ -10,13 +9,6 @@ namespace Sample04.Activities
 {
     public abstract class ArithmeticOperation : Activity
     {
-        private readonly IWorkflowExpressionEvaluator evaluator;
-
-        protected ArithmeticOperation(IWorkflowExpressionEvaluator evaluator)
-        {
-            this.evaluator = evaluator;
-        }
-
         public WorkflowExpression<double[]> Values
         {
             get => GetState<WorkflowExpression<double[]>>();
@@ -31,7 +23,7 @@ namespace Sample04.Activities
 
         protected override async Task<ActivityExecutionResult> OnExecuteAsync(WorkflowExecutionContext context, CancellationToken cancellationToken)
         {
-            var values = await evaluator.EvaluateAsync(Values, context, cancellationToken);
+            var values = await context.EvaluateAsync(Values, cancellationToken);
             var sum = Calculate(values);
 
             context.SetLastResult(sum);
diff --git a/src/samples/Sample04/Activities/Divide.cs b/src/samples/Sample04/Activities/Divide.cs
index e3868624d..d2d40a73c 100644
--- a/src/samples/Sample04/Activities/Divide.cs
+++ b/src/samples/Sample04/Activities/Divide.cs
@@ -1,14 +1,9 @@
 using System.Linq;
-using Elsa.Services;
 
 namespace Sample04.Activities
 {
     public class Divide : ArithmeticOperation
     {
-        public Divide(IWorkflowExpressionEvaluator evaluator) : base(evaluator)
-        {
-        }
-
         protected override double Calculate(params double[] values) => values.Aggregate((left, right) => left / right);
     }
 }
\ No newline at end of file
diff --git a/src/samples/Sample04/Activities/Multiply.cs b/src/samples/Sample04/Activities/Multiply.cs
index 2073134b3..dec62f74d 100644
--- a/src/samples/Sample04/Activities/Multiply.cs
+++ b/src/samples/Sample04/Activities/Multiply.cs
@@ -1,14 +1,9 @@
 using System.Linq;
-using Elsa.Services;
 
 namespace Sample04.Activities
 {
     public class Multiply : ArithmeticOperation
     {
-        public Multiply(IWorkflowExpressionEvaluator evaluator) : base(evaluator)
-        {
-        }
-
         protected override double Calculate(params double[] values) => values.Aggregate((left, right) => left * right);
     }
 }
\ No newline at end of file
diff --git a/src/samples/Sample04/Activities/Subtract.cs b/src/samples/Sample04/Activities/Subtract.cs
index 68e9ff62b..987202c51 100644
--- a/src/samples/Sample04/Activities/Subtract.cs
+++ b/src/samples/Sample04/Activities/Subtract.cs
@@ -1,14 +1,9 @@
 using System.Linq;
-using Elsa.Services;
 
 namespace Sample04.Activities
 {
     public class Subtract : ArithmeticOperation
     {
-        public Subtract(IWorkflowExpressionEvaluator evaluator) : base(evaluator)
-        {
-        }
-
         protected override double Calculate(params double[] values) => values.Aggregate((left, right) => left - right);
     }
 }
\ No newline at end of file
diff --git a/src/samples/Sample04/Activities/Sum.cs b/src/samples/Sample04/Activities/Sum.cs
index e00412c51..99a10cf4f 100644
--- a/src/samples/Sample04/Activities/Sum.cs
+++ b/src/samples/Sample04/Activities/Sum.cs
@@ -1,14 +1,9 @@
 using System.Linq;
-using Elsa.Services;
 
 namespace Sample04.Activities
 {
     public class Sum : ArithmeticOperation
     {
-        public Sum(IWorkflowExpressionEvaluator evaluator) : base(evaluator)
-        {
-        }
-
         protected override double Calculate(params double[] values) => values.Sum();
     }
 }
\ No newline at end of file