done : )

src/main/java/rocks/zipcode/calcskin/CalcEngine.java

@@ -11,16 +11,18 @@ public class CalcEngine {
     }
 
     public double subtract(double v, double v1) {
-        return Double.NaN;
+        return v - v1;
     }
 
     public double multiply(double v, double v1)
     {
-        return Double.NaN;
+        return v * v1;
     }
 
     public double divide(double v, double v1) {
 
-        return Double.NaN;
+        return v / v1;
+
+
     }
 }