1) You should not use any formula that you do not understand.
2) Why would you want to use a single-payment formula for a series of payments?
3) What do you know about RRSPs?
4) You must make up your mind what you mean. Do you make a deposit at the beginning or at the end of each period? It makes a difference. If deposits are at the end of each period, there is NO interest in the last deposit.