Answer: Hello mate!
we have the equation 3x-7y=-28 and we want to solve it for y.
This is equivalent to isolate y in one side of the equation, lets do this:
3x-7y=-28
we subtract 3x in both sides of the equation.
3x -7y -3x = -28 - 3x
-7y = -28 - 3x
now we can divide both sides by -7.
-7y/(-7) = (-28 - 3x)/-7
y = (28 + 3x)/7 = (3/7)x + 4
And now there is the equation y(x).