Find the approximate value of x that makes fx=gx

Question

Fx=400(0.91)^x

Gx=40(1.09)^x

The value of x that makes f(x)=g(x) is x=

Answer 1

400(0.91)^x = 40(1.09)^x

10 = (1.09)^x / (0.91)^x

10 = (1.1978)^x

log 10 = x log 1.1978

1 = 0.0783 x

12.75 = x