math homework help please!?

I have this 20 question assignment but i have 5 questions that I don't understand..

1. The Trustees of a college have accepted a gift of $350000, but are required to deposit it in an account paying 12% per year, compounded semiannually. They may make equal withdrawals at the end of each six-month period, nut the money must last 5 years

A) find the amount of each withdrawal

B) find the amount of each withdrawal if the money must last 6 years

2. A couple took out a 30-year mortgage for $181,558 at 12.3% compounded monthly. After they had made 10 years of payments (120 payments) they decided to refinance the remaining loan balance for 25 years at 5.1% interest, compounded monthly. What will be the balance on their loan 6 years after they refinance?

3. A building contractor gives a $15000 promissory note to a plumber who has loaned him $15,000. The note is due in 9 months with interest at 8%. Three months after the note is signed, the plumber sells it to a bank. If the bank gets 9% return on it's investment, how much will the plumber receive? Will it be enough to pay a bill for $15,236?

4. Starting at age 50, a woman puts $1700 at the end of each quarter into retirement account that pays 7% interest compounded quarterly. When she reaches the age of 60, she withdrawals the entire amount and places it in a mutual fund account that pays 9% compounded monthly. From then on she deposits $300 in the same mutual fund at the end of each month. How much is in the account when she reaches the age of 65?

5. A new employee charged $9080 on his credit card to relocate for his first job. After noticing that the interest rate for his balance was 18% compounded monthly, he stopped charging on that account. He wishes to pay off his balance in 4 years using automatic payments sent at the end of each month.

A) what monthly payment must he make to pay off the account at the end of 4 years?

B) how much interest will he have paid?