Given:
Motorcycle price - $23,100
Downpayment - $4,200
Monthly payments - $339.62
No. of years = 5 years
Find: Total amount paid and interest added
Solution:
a. total amount paid (monthly payments + downpayment)
In 5 years, there are 12 x 5 = 60 months. To be able to calculate the total paid monthly payments through out the 5 years, let's multiply 60 months to the monthly payment of $339.62.

The total paid monthly payments is $20, 377.20. Since Jenny paid a dwonpayment of $4, 200;

Jenny ended up paying a total amount of $24, 577.20 for the motorcycle.
b. interest added on the loan
Since Jenny had made a downpayment of $4200, the remaining balance on the motorcycle is:

Thus, she only loan $18,900.
Out from this $18,900, she made a total monthly payment of $20, 377.20. Hence, the interest added is:

The interest added on the loan is $1,477.20.