Add area calculation alert to percentage exercise

Author: HadiVahidi20

Sprint-1/prep/percentage.html

@@ -132,5 +132,11 @@ <h3 id="areaResult"></h3>
      }
 
     })
+    
+    const width= 5;
+    const height=4;
+
+    alert ("area is "+ width* height );
+
 
 </script>