I've got this question on challange and I don't understand how 13 comes in output. Guyzz plz explain if you understand

Question

int [] a= {4,2,3 };
for (int i= 0 ; i <3 ; i++ ) {
a[0] += a[i] ;
}
System. out.print(a[0]);

Answer 1

a [0] = a [0] + a [0] + a [1] + a [2]

Answer 2

Ok ri8, thanks Calvin.