diff --git a/2-csharp/lesson-6-projects/challenge-project/Starter/Program.cs b/2-csharp/lesson-6-projects/challenge-project/Starter/Program.cs
index b769206..9d481f3 100644
--- a/2-csharp/lesson-6-projects/challenge-project/Starter/Program.cs
+++ b/2-csharp/lesson-6-projects/challenge-project/Starter/Program.cs
@@ -17,7 +17,6 @@ is used to ensure that logic in the MakeChange method is working as
 expected.
 */
 
-
 string? readResult = null;
 bool useTestData = false;
 
@@ -115,10 +114,10 @@ static void LoadTillEachMorning(int[,] registerDailyStartingCash, int[] cashTill
 
 static void MakeChange(int cost, int[] cashTill, int twenties, int tens = 0, int fives = 0, int ones = 0)
 {
-    cashTill[3] += twenties;
-    cashTill[2] += tens;
-    cashTill[1] += fives;
-    cashTill[0] += ones;
+    int availableTwenties = cashTill[3] + twenties;
+    int availableTens = cashTill[2] + tens;
+    int availableFives = cashTill[1] + fives;
+    int availableOnes = cashTill[0] + ones;
 
     int amountPaid = twenties * 20 + tens * 10 + fives * 5 + ones;
     int changeNeeded = amountPaid - cost;
@@ -130,28 +129,28 @@ static void MakeChange(int cost, int[] cashTill, int twenties, int tens = 0, int
 
     while ((changeNeeded > 19) && (cashTill[3] > 0))
     {
-        cashTill[3]--;
+        availableTwenties--;
         changeNeeded -= 20;
         Console.WriteLine("\t A twenty");
     }
 
     while ((changeNeeded > 9) && (cashTill[2] > 0))
     {
-        cashTill[2]--;
+        availableTens--;
         changeNeeded -= 10;
         Console.WriteLine("\t A ten");
     }
 
     while ((changeNeeded > 4) && (cashTill[1] > 0))
     {
-        cashTill[1]--;
+        availableFives--;
         changeNeeded -= 5;
         Console.WriteLine("\t A five");
     }
 
     while ((changeNeeded > 0) && (cashTill[0] > 0))
     {
-        cashTill[0]--;
+        availableOnes--;
         changeNeeded -= 1;
         Console.WriteLine("\t A one");
     }
@@ -159,6 +158,11 @@ static void MakeChange(int cost, int[] cashTill, int twenties, int tens = 0, int
     if (changeNeeded > 0)
         throw new InvalidOperationException("InvalidOperationException: The till is unable to make change for the cash provided.");
 
+    cashTill[3] = availableTwenties;
+    cashTill[2] = availableTens;
+    cashTill[1] = availableFives;
+    cashTill[0]= availableOnes;
+
 }
 
 static void LogTillStatus(int[] cashTill)
diff --git a/2-csharp/lesson-6-projects/challenge-project/Starter/Starter.csproj b/2-csharp/lesson-6-projects/challenge-project/Starter/Starter.csproj
index f02677b..74abf5c 100644
--- a/2-csharp/lesson-6-projects/challenge-project/Starter/Starter.csproj
+++ b/2-csharp/lesson-6-projects/challenge-project/Starter/Starter.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>