if the nth term of a GP is 128 and the sum of its n terms is 225.if the common ratio is 2, then the first term of the GP is????

let 1st term be a
last term= 128  , sum of n terms = 255 , common ratio  =2
a.r^n-1 = a.(2)^n-1 = 128
a/q
Sn = lr - a / r -1
255 = 128 * 2 - a / 2 - 1
255 = 256 -a 
256 - 255 = a
therefor a = 1(ans)