The fifth term of a GP is 81 and first term is 16. Find the 4th term.?

The nth term of a GP is ar^{n - 1} ,
5th term = ar^{5 - 1} = ar⁴ = 81
1st term = a = 16
∴ r⁴ = 81/16
⇒ r = ∜81/16 = 3/2
∴ 4th term = ar^{4 - 1} = ar³ = 16 x 3/2 x 3/2 x 3/2 = 54