$\"\"$

If a principal $\"\"$ is invested at an annual interest rate $\"\"$ compounded $\"\"$ times a year, then the balance $\"\"$ in the account after $\"\"$ years is $\"\"$ .

Since investment is compounded monthly, $\"\"$ .

Investment become triple means $\"\"$ .

Substitute $\"\"$ and $\"\"$ in $\"\"$ .

$\"\"$

Apply logarithm on each side.

$\"\"$

Apply power property of logarithm : $\"\"$ .

$\"\"$

Investment triple in $\"\"$ of time.

$\"\"$

Investment triple in $\"\"$ of time.