This is already solved for y. Assuming you want to solve for x:
y = -5x - 1
-5x - 1 = y
-5x = y + 1
x = (y + 1) / (-5)
x = - (y + 1) / 5
If, in the original equation, you want a specific number for y, you must first provide a specific value for x, then do the calculations. "y" has different values, for different values of "x".
-y + y equals 0.
For y - 2y - 3y equals 0, y equals 0.
b = y - mx.
y= -2x
y - 3 = 0 y = 3
y=x+4
y = -6
-3
y=5-x
16
y = mx + b
2y = 4 (divide both sides by 2 to solve) y = 2