Question

how to take out time in compound intrest

Answer 1

You know the formula right? Time is power in the formula..... If amount principal and rate are given we can form a equation with time as a variable. then we simplify the remaining part.
after that we get the base of the power(time) and other side of equation.
EXAMPLE - suppose LHS is (9/8)^x and RHS is 81/64 then we can rewrite RHS as (9/8)^2

${ \frac{9}{8} }^{x} = { \frac{9}{8} }^{2}$
by observing bases are same powers must also be same..
so x=2
that is 2 years