Question

let me send a picture of the question

Answer 1

You have the following formula for the sum Sn:

$S_n=\frac{a_1-a_nr}{1-r}$

a1 = 4

an = 128

r = 2

replace the previous values into the formula for Sn:

$S_n=\frac{4-128\cdot2}{1-2}=252$

Hence, the asnwer to Sn is 252