a) We would apply the formula for determining compound interest which is expressed as
A = P(1 + r/n)^nt
where
A = the total amount in the account at the end of t years
r = interest rate
n = the periodic interval at which it was compounded
P = the principal or initial amount deposited
From the information given,
P = 1500
r = 1.8/100 = 0.018
n = 1 because it is compounded once in a year
Thus, an equation to represent the amount of money in the account as a function of time in years ia
A = 1500(1 + 0.018/1)^1 * t
A = 1500(1.018)^t
B) If t = 20, then
A = 1500(1.018)^20
A = 2143.12
The interest earned would be the total amount - the principal
Interest earned after 20 years = 2143.12 - 1500 = 643.12
If t = 10, then
A = 1500(1.018)^10
A = 1792.95
Interest earned after 10 years = 1792.95 - 1500 = 292.95
Thus, the difference in interest earned between both years is
643.12 - 292.95
= $350.17