f(a)=3a+1------------------(1)
g(a)=2a^3-4-2a----------------(2)
find f(g(2a))
g(2a) = 2* (2a)^3 -4 - 2*(2a)
= 2* 2a*2a*2a - 4 - 4a
= 16 a^3 -4a -4 ---------------(3)
f[g(2a)] = f [16 a^3 - 4a -4] { from (3) }
= 3*(16 a^3 - 4a -4) + 1 { from (1) }
= 48 a^3 - 12a -12 + 1
= 48 a^3 -12a -11