Precalculus, Chapter 9, 9.3, Section 9.3, Problem 44

You need to write the following formula such that:
a_5 = a_2*q^3
You need to evaluate q and a_1 , such that:
q^3 = (a_5)/(a_2) => q^3 = (3/64)/3 => q = 1/4
a_2 = a_1*q => a_1 = (a_2)/q => a_1 = 3/(1/4)=> a_1 =12
Hence, evaluating a_1 yields a_1 = 12.