This problem was worth 400 points and was the 4th in a series of classroom or school themed problems in the crypto category. English class, Science Class, History Class, Math Class and finally Report Card were the series of five challenges, worth 100,200,300,400 and 500 points. We did successfully solve Science and History for those 500 points.

Original writeup (http://wclaymoody.com/blog/2017/11/rc3ctf-2017-math-class).