f(3) = 4 f(f(3)) = f(4) = 8
To compute f(3), do a hand simulation, keeping track of the values of the variable.
k x --- --- 1 3 2 4The loop keeps going as long as k is less than or equal to x. Each time, it doubles k. The loop ends when k > x.
To compute f(4), do another hand simulation.
k x --- --- 1 4 2 4 8Again, if k is less than or equal to x, the loop doubles k and goes to the top again.