Completed lab.

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

@@ -6,18 +6,22 @@ public class CalcEngine {
     }
 
     public double add(double v, double v1) {
-        return Double.NaN;
+        double add = v + v1;
+        return add;
     }
 
     public double subtract(double v, double v1) {
-        return Double.NaN;
+        double sub = v - v1;
+        return sub;
     }
 
     public double multiply(double v, double v1) {
-        return Double.NaN;
+        double product = v * v1;
+        return product;
     }
 
     public double divide(double v, double v1) {
-        return Double.NaN;
+        double div = v / v1;
+        return div;
     }
 }

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

@@ -24,10 +24,10 @@ public class CalcSkin extends Application {
         launch(args);
     }
     private static final String[][] template = {
-            { "7", "8", "9", "/" },
-            { "4", "5", "6", "*" },
-            { "1", "2", "3", "-" },
-            { "0", "c", "=", "+" }
+            {"7", "8", "9", "/" },
+            {"4", "5", "6", "*" },
+            {"1", "2", "3", "-" },
+            {"0", "c", "=", "+" }
     };
 
     private final Map<String, Button> accelerators = new HashMap<>();
@@ -50,7 +50,7 @@ public class CalcSkin extends Application {
         final TextField screen  = createScreen();
         final TilePane  buttons = createButtons();
 
-        stage.setTitle("Calc");
+        stage.setTitle("Calculator");
         stage.initStyle(StageStyle.UTILITY);
         stage.setResizable(false);
         stage.setScene(new Scene(createLayout(screen, buttons)));

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

@@ -5,7 +5,6 @@ import rocks.zipcode.calcskin.CalcSkin;
 // You probably should make NO changes here. Keep it simple.
 public class MainApplication {
     public static void main(String[] args){
-
         CalcSkin.launchCalc(args);
     }