The average student college loan rate is 4%. You borrowed $18,000 per year for 4 years for tuition, room, & board. If the interest is computed as simple interest, annually, how much interest will you owe when you graduate. Assume 4 years interest on the freshman year loan, 3 years on the sophomore loan, 2 years on the junior loan, and 1 year on the senior loan.
a) $7,200
b) $18,720
c) $19,468
d) $78,240