First, change percent into decimal value
Percent means per hundred
APR = 3.5%
APR = 3.5/100
APR = 0.035
The APR is 0.035 of the total loan
Second, we need to find interest rate for 9 months
interest rate = 9/12 × 0.035
interest rate = 3/4 × 0.035
interest rate = 0.75 × 0.035
Third, determine what to put into calculator
She can put it like this
interest = interest rate × total loan
interest = 0.75 × 0.035 × 2,800
Or she can put it like this
interest = 0.02625 × 2,800