Javascript for loop add a number x times : Hi could need som help with this problem. 

  
Exercise:
 
 * Use a for-loop to increment 399 with the value 8, 13 times.


My Code so far. 
When i run it i get Error, could any one help me in the right direction? 

thank you!

>     var a = 399;  
>     var b = 8;
>     
>     for (i = 0; i < 13; i++) {  
>       a += b; 
>     }
>     
>     ANSWER = a;

