why out put is 55

Question

Hi, I'm really confused why the output of this code is 55, if you can explain thanks
class MyClass {
public static void main (String [] args) {
int result = sum (10);
System.out.println (result); }
public static int sum (int k) {
if (k> 0) { return k + sum (k - 1);
}
else { return 0; } } }

Answer 1

Recursion

Answer 2

Recursion

sum(10)
= 10 + sum(9)
= 10 + 9 + sum(8)
....

until sum(0) return 0

Answer 3

Thank you so much