Math Problem Generator gives a video about how to add and subtract variables. All you have to do is combine the coefficient, which is the number that comes before the variable. The numbers are added or subtracted but the variable remains the same. In the video, the example given is 9x + 6x - x. First you add 9x + 6x, giving you 15x. The equation is now 15x - x. If a variable has no number written in front of it, that means the value is 1. So the equation is 15x - 1x and that is equal to 14x.
The video is an easy way to learn how to add and subtract variables. It teaches you everything step by step and provides an on screen equation so that it's easier for you to master the technique.