Hi

The first three terms of a geometric progression are $\displaystyle 2^n$, 2^(n+1),2^(n+2).

(a) Find n.

(b) Find the sum of the first 6 terms. Express your answer as a rational number.

Could someone please show me how to do (a)? I only know the basics of geometric progression (i.e. the formulas) but none of them fit this question somehow.