I love your app, and you probably should not be allowed to divide by 'x'
I recently purchased dragonbox2 as a parent and while working through the problems found that the chapter 4-20 problem called for dividing by 'x'. The issue with this being you do not know the value for 'x' and could therefore unknowingly be dividing by 0 and end up missing potential solutions. This message board explains this in better detail:
Dividing by a variable is generally a 'bad habit' that should be avoided.
There goes my unit on rational functions.