Answer:
The correct answer is: Interest on interest.
Explanation:
Interest on interest is the percentage obtained out of an initial investment after the initial amount plus interest (the total) is invested one more time. Interest on interest is also called Compound Interest. The term is often used when talking about bonds.
Just like in Art's case, the initial investment was $100 earning $8 the first year. He reinvested $108 and earned an additional $8.64 for the second year. The $0.64 represents his interest on interest.