We can get rid of the + c by putting it on the other side. When a number goes to the other side it does the opposite, so the - will become a +. It will end up as:
y + c = mx
We just need x on itself so we need to get ride of m. In this sum, mx means that they are multiplying together, we need to make that divide. So we take m on the other side and make it divide. This brings us to x on itself.
