To calculate the compound interest you have to use the following formula
Where
A: accrued amount → is the principal amount + interest acquired
P: principal amount
t: time in years
n: number of compounding periods
r: interest rate, expressed as a decimal number
For this exercise
P= $500.00
r=0.13
t=3years
n→ is a monthly compound, which means that there are 12 compounding periods per year: 12*3=36 in 3 years there will be 36 periods
The total amount is