Graham had to pay $22,000 of student loans when he graduated. by the following year, his debt had been reduced to $15,200. how much of his debt did he pay off during that year?

Alright, This one is fairly simple its just some Subtracting :)

Graham has to pay $22,000

Well if his debt went from $22,000 to $15,200

He had to of paid some off

So let me put down the Equation, It's very simple ( The word problem could be hard though).

$22,000 - $15,200 this Equals $6,800

He Paid $6,800 in the Following year.

Therefore Your Answer Would be $6,800  :)