4. [5+5=10 mark] After winning a photography contest, Sophie invested $7,000 ve years ago into a savings account which has since paid interest at a nominal rate compounded semiannually. 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 semiannually? Round your answer up to the nearest multiple of 6