Teacher Takes Student's Phone, Sets Passcode as Math Problem Answer

This is what you want from a math teacher. The word problem you see here is what happened after a Redditor's "friend" was caught using his phone during math class. The teacher confiscated the phone, and set the passcode to a certain number, found by answering the problem.

It reads:

A car dealer offers Lachlan a car that is priced at $21,800, but he only has a $600 deposit. Lachlan trade in is actually worth $500. The finance company insists on a 10% deposit for a 22% flat rate deal, so the dealer inflates the prices of both the trade-in and the car purchased What are the inflated prices, and what is the monthly repayment to pay of the car in 4 years?

Monthly payment rounded to the nearest dollor [sic]

First number is 0

I have no idea where to even start with that. Good luck, kid. [Reddit via Flowing Data]