Jared bought a new amplifier for his guitar by borrowing the money from his mom. The amplifier cost $235. Jared is paying his mom back $18 each week. If Jared still owes his mom $73, how many weeks has he been paying her back?

Jared has already paid his mother the following sum of money:

235 - 18 = 217
235 - 73 = 162
73 + 18 = 91