mantel attack on handsome boys

$C=A \times GP^{2}$ so $GP^{2}=\frac{12}{3}=4$ therefore GP is 2 or -2 as B could be 6 or -6

In General you could write a Geometric Sequence like this:

{a, ar, ar^2, ar^3, ... }

where r is the common ratio of the GP

{A,B,C,.....} here A = 3 , B = ? C= 12 well we know that C represent ar^2, so r becomes = 2