If you would like to transform the equation 6x + 2y = 15 into the equation 0 = 15 - 6x - 2y, you have to do two following steps or you can do this at the same time (and you have to do just one step).
First, you have to subtract 6x from both sides of the equation:
6x + 2y = 15 /-6x
6x + 2y - 6x = 15 - 6x
2y = 15 - 6x
Second, you have to subtract 2y from both sides of the equation:
2y = 15 - 6x /-2y
2y - 2y = 15 - 6x - 2y
The result:
0 = 15 - 6x - 2y
