see here
https://www.physicsforums.com/threads/in-discrete-math-adv-counting-techniques-see-picture-h.882371/
somehow forum disabled comments so created new post:
basically is easy to take the problems given recursive formula, find a, b, d, c and replace but how to the math for
a^k
g(n/b^j)...
PLEASE click PICTURE to Expand and zoom in , EXAMPLE 5 is end in one paragraph - is the last example the general forumula applies Rosen, Discrete Math and Appl e7 ch.8, Mcgraw hill