27,000 in three years at 6% interest compounded monthly how much do I need to invest.

6% annually, I assume, not 6% monthly


Calculation programs are all over the net. Your answer is $22,600 give or take a few dollars. Had to contribute $1 once a year.
http://www.bankrate.com/calculators/retirement/investment-goal-calculator.aspx

(If someone says they can earn 6% monthly, you are being scammed.)

Looks like a homework problem.