public int mystery(int b)
{
    if (b == 0)
        return 0;
    
    if (b % 2 == 0)
        return mystery(b - 1) + 3; // call 1
    else
        return mystery(b - 1) + 2; // call 2
                                   // finished call 2, got back 5
                                   // adds 2
                                   // stops and returns 7
}

Call stack

m(0)   returns 0
m(1)   returns 2
m(2)   returns 5
m(3)   returns 7
m(4)1
m(5)2

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