$\"\"$

The equation for the amount for monthly compound interest is $\"\"$ .

Interest rate is $\"\"$ and time $\"\"$ years.

Amount available for retirement in $\"\"$ years is $ $\"\"$ .

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

$\"\"$

$\"\"$ .

Principal amount invested is $\"\"$ .

$\"\"$

Principal amount invested is $\"\"$ .