Question 1176312
The nth term of a G.P. is a_n = a*r^(n-1), where a is the 1st term and r is the 
common ratio.
Since a_5 = 9*a_3, we have ar^4 = 9ar^2 -> r^2 = 9
There are two possibilities: r = 3, or r = -3
If r = 3, a_6 + a_7 = 1944 = a(3)^5 + a(3)^6 -> a = 1944/((3)^5 + (3)^6)) = 2
If r = -3, a = 1944/((-3)^5 + (-3)^6) = 4