If you buy a computer directly from the manufacturer for $ 2,469 and agree to repay it in 48 equal installments at 2.1 % interest per month on the unpaid balance, how much are your monthly payments? how much total interest will be paid?

Monthly installments/payments, P = C*D
C = cost = $2,469
D = (i/12)/[1-(1+i/12)^-48] = (0.021/21)/[1-(1+0.021/12)^-48] = 0.0217

Therefore;
P = 2469*0.0217 = $53.67

Total interest paid, I = Total amount paid - Cost
Total amount paid = P*48 = 53.67*48 = $2,576.30

Then,
I = 2576.30-2469 = $107.30