Hello there! So, the formula for compound interest is P(1 + r/n)^nt. P = principal, r = rate, n = number of times compounded per year, and t = time in years.
a. Just by looking at the numbers, I would say that Gavin should take the first option of 9% compound interest annually.
b. I say this, because you're gonna earn a lot more. Just by solving the question for the amount in 5 years for each account, the first opinion will earn you $3,077.35, and the other option will only give you $2,265.42 in 5 years. Keep in mind that compounding quarterly means 4 times per year. With a low interest rate, it's no surprise that the first option would be a better choice.