This is a beginners discrete math problem where I have no id

This is a beginners discrete math problem where I have no idea how to solve it without a calculator.

Find f(150), where f(n) is defined recursively by f(0) = 0 and for n = 0, 1, 2,…, as the following:
1.)  f(n+1) = 2*f(n)
2.)  f(n+1) = (f(n))^3
3.)  f(n+1) = f(n) + 2

Solution

1) f(0) = 0

    f(1) = 2 x f(0) = 2 x 0 = 0

    f(2) = 2 x f(1) = 2 x 0 = 0

f(3) = 2 x f(2) = 2 x 0 = 0

likewise, f(4), f(5) ,......f(147), f(148), f(149) = 0

so, f(150) = 2 x f(149) = 2 x 0 = 0

2) f(1) = f(0)^3 = 0

    f(2) = f(1)^3 = 0

    f(3) = f(2)^3 = 0

likewise, f(4), f(5) ,......f(147), f(148), f(149) = 0

    f(150) = f(149)^3 = 0

3) f(1) = f(o) + 2 = 0 + 2 = 2

    f(2) = f(1) + 2 = 2 + 2 = 4

    f(3) = f(3) + 2 = 4 + 2 = 6

   so, f(n) = 2n

        f(150) = 2 x 150 = 300