Solving T(n) = 2*T(n-1)+4 witht the Master Theorem
By expansion you can see it is $T(n) = \Theta(2^n)$ (suppose $T(1) = 1$):
$$
T(n) = 2T(n-1) +4 = 2(2T(n-2)+4) + 4 = 2^2T(n-2) + 2\times 4 + 4 = \ldots =
$$
$$
2^{n-1}T(1) + 2^{n-2}4 + \cdots + 4 = 4\left(\sum_{i=1}^{n-1}2^i\right) = 4(2^n - 1)
$$