Answer:
9
Step-by-step explanation:
30×(1.14^x) = 400×(0.86^x)
400/30 = (1.14^x)/(0.86^x)
40/3 = [1.14/0.86]^x
Apply logs both sides with any base, I'm using log base 10 which is lg.
lg(40/3) = lg[1.14/0.86]^x
lg(40/3) = x × lg[1.14/0.86]
x = lg(40/3) ÷ lg[1.14/0.86]
x = 9.19
Nearest integer, x = 9