Answer:
Monthly Payment on the Mortgage :
P = L[c(1 + c)n]/[(1 + c)n - 1]
Where, P = Monthly Payment,
L = Loan Amount => $90,000
C = Monthly Interest Rate => 4.5%/12 = 0.375%
n = Number of months. => 15 x 12 = 180 Months
$90,000[0.375%(1+0.375%)180]/[(1+0.375%)180-1] = $688.49
Remaining Loan balance after P months:
B = L[(1 + c)n - (1 + c)p]/[(1 + c)n - 1]
After 80 Months:
=> $90,000[(1+0.375%)180-(1+0.375%)80]/[(1+0.375%)180-1] = $57,324.65
After 110 Months:
=> $90,000[(1+0.375%)180-(1+0.375%)110]/[(1+0.375%)180-1] = $42,318.68
Now, total payment made in the 80th month = $688.49 x 80 = $55,079.2
Total Payment made in the principal = $90,000 - $57,324.65 = $32,675
Total Interest Paid = $55,079.2 - $32,675 = $22,403.85
Total payment made in the 110th month = $688.49 x 110 = $75,733.90
Total Payment made in the principal = $90,000 - $42,318.68 = $47,681.32
Total Interest Paid = $75,733.90 - $47,681.32 = $28,052.58