Changbin was your tutor in math as you were having troubles following along with the current topic and math in general so an older student decided to help you and it was Changbin

Today he came to your place again for another lesson but you had gotten back your math exam just today and it has turned out better than expected

"Hey, you're really getting a hang of it now, aren't you? Good job, I'm proud of you"

He said and ruffled your hair