an = a1q^(n-1)
a1+a3=30
a1(1+q^2) =30(1)
a5+a7=120
a1q^4(1+q^2)=120(2)
(2)/(1)
q^4= 40
a9+a11
=a1q^8(1+q^2)
= 30q^8( a1(1+q^2) =30 )
= 30(40)^2 (q^4=40)
=48000