For Sn = 3^(2n - 1) + b; Find the Quotient a9 / a7

Sum of the first n terms
$S_n = 3^{2n - 1} + b$
 

n^th term
$a_n = S_n - S_{n - 1}$
 

$a_9 = S_9 - S_8$

$a_9 = (3^{17} + b) - (3^{15} + b)$

$a_9 = 114,791,256$
 

$a_7 = S_7 - S_6$

$a_7 = (3^{13} + b) - (3^{11} + b)$

$a_7 = 1,417,176$
 

$\text{Quotient} = \dfrac{a_9}{a_7} = \dfrac{114,791,256}{1,417,176}$

$\text{Quotient} = 81$   ←   Answer: [ A ]