The formula for simple interest is A = P(1+rt)
Where P is the principal ( amount of money deposited)
R is the interest rate
t is the amount of time
A is the total of the principal and interest.
Using the information given in the problem:
A = 4200(1+0.0325*3)
A = 4200(1 + 0.0975)
A = 4200(1.0975)
A = 4609.50
Now subtract the principal from the total to find the amount of interest:
4609.50 - 4200 = 409.50
Amount of interest = $409.50