i need help on how to solve this

4. [5+5=10 mark] After winning a photography contest, Sophie invested $7,000 five years ago into a savings account which has since paid interest at a nominal rate compounded semi-annually. Her investment is now worth $8532.96. (a) /5 mark/ Find the nominal interest rate per year. (b) /5 mark/ How many months will it take $7,000 to grow to $15,000 at an interest rate of 4% compounded semi-annually? Round your answer up to the nearest multiple of 6