Hi, i am trying to rewrite this problem as a geometric series in order to solve it but im having some problems. 4^(k+2)/7^(k-1). from there i get 112(4^k/7^k) which seems fine to me with a=112 and r=(4/7), but my book has a=64 and r=(4/7). Can someone please teel me if i did something wrong or what is happening?

Thank you.