Jerry has a credit card debt of $15,600 that he would like to reduce by applying $8,500 of his inheritance money to the balance. in addition, he would like to modify his debt payment plan to pay off the remaining balance in 24 months rather than 60 months. his credit card has an apr of 18%. how much will these changes save jerry in finance charges (interest)?

First we need to solve the finance charge without the changes.
B = A (1 + ti)
where
t is the number of years, 60 months or 5years
i is the interest rate per year, 18% or 0.18
A is the principal amount, %15,600
B is the amount after t years
so,
B =$15,600 ( 1 + 0.18 x 5 )
B = $15,600 ( 1 + 0.9 )
B= $15,600 (1.9)
B= $29,640.
The finance charge without the changes is $29,640(amount after 5 years) - $15,600(principal amount)  = $14,040.

Applying the changes, the principal amount would be $15,600 - $8,500 = $7,100, the number of years will be 2 years (24 months)in equation
B = $7,100 (1 + 0.18 x 2)
B = $7,100 (1 + 0.36)
B = $7,100 (1.36)
B = $9,656, the finance charge with the changes is $9,656 - $7,100 = $2,556.

The changes Jerry made can save $14,040 - $2,556 = $11,484.