One math question

An employee has contributed with her employer to a retirement plan. At the date of her retirement, the total retirement benefits are $250,000. The retirement program provides for investment of this sum at an interest rate of 12 percent per year compounded semiannually. Semiannual disbursements will be made for 30 years to the employee or, in the event of her death, to her heirs.
a) What semiannual payment should be generated?
b) How much interest will be earned on the $250,000 over the 30 years?

Ans:
a)$15,470
b)$678,200

Thank you.