solve:-
Here,
a₆ = ar⁵ = 1215 .............. 1
and,
a₁₀ = ar⁹ = 98415 .............. 2

Dividing equation (2) by (1), we get.

[ar⁹]/[ar⁵] = [98415]/[1215]
=> r⁴ = 81
=> r⁴ = 3⁴
=> r = 3

Equation (1) we get
ar⁵ = 1215
=> a3⁵ = 1215
=> a * 243 = 1215
=> a = 1215 / 243
=> a = 5
ie. a = 5 and r = 3

Now,
Here, first term = 5,
common ratio = 3
then,
15^th term is = 5*3 ^{(15 - 1)}
= 5*3 ¹⁴
= 5*4782969
=> 15^th term is = 23914845