If I won the lottery and was awarded $3,000,000 and promised

If I won the lottery and was awarded $3,000,000 and promised to be paid in 15 years from today. Since the payment is guaranteed by the state that I live I could sell the claim today for an immediate single cash payment.
What is the least I could sell the claim for if I earned the following rates of return on a similar-risk investment during the 12 year period:

6%?
7%?
8%?

I am not sure what formula to use here if it is present value or future value.