Hello once again. Im really confused with the two sequences and series question. Can somebody please help me ?

1. The 2nd and 4th terms of a geometric series is 36 an 16 respectively. All the terms are positive. Determine the first term.

2. The floowing series is given :

(x-1) + (x-1)^{2 }+ (x-1)^{3}

2.1 for which values of x will the series converge ?

3.

n

Σ(3-4k) = -125

k=1

where k =1. determine the value of n.