please explain why the function times10 work.

1 2 '* Computes and returns "'10 * a' without using * multiplication. 3 */ 4 int times 10 (int a) { // input: int a, output: an int 20 Chapter 1. Memory: The Stack int X , a // local variables // 2 * // 4 * a // 8 * // 2*a + 8*a 10*a a == 5 y; 6 X a + a; 7 y = X + x; 8 y = y + y; 9 return + y; 10} 11 12 int main() { 13 int n = 42; 14 n = times 10 (n); 15 return 0; 16 } // n is local to main