Melody is much better at these questions than me, but here is my 'guess'
Since a geometric series can be expressed as a1 + a1 r + a1r^2 + a1 r^3
we can see that r = 3/a from the terms given
the SUM of a geometric series is S = a1 / (1-r)
S = a1 /(1-r)
= 4/(1-r) needs to be a perfct square....
by brute force solving this equation with S= perfect square , '9' will not work , but '16' will
16 = 4/ (1- 3/a)
16- 48/a = 4
48/a = 12
a = 4 Correct???
