If you are given y = (-3/7)x - 2 and you want it in the form Ax+By = C, then...
y = (-3/7)x-2
7*y = 7*( (-3/7)x-2) ... multiply both sides by 7
7y = -3x-14 ... distribute and multiply
7y+3x = -3x-14+3x ... add 3x to both sides
3x+7y = -14
The standard form equation is 3x+7y = -14