I am trying to set up a spreadsheet function to get the following answers
but am having little luck. Can anyone point me in the right direction for a
formula to get the required answers?

Q: Consider a bond with a face value of $1,000. The coupon payment is made
semi-annually and the yield to maturity is 12% (effective annual yield). How
much would you pay for the bond if:
A: The coupon rate is 8% and the time to maturity is 20 years?
B: The coupon rate is 10% and the time to maturity is 15 years?

Any help would be appreciated...