y = mx + b
where m is the slope and b is the y-intercept.
1. 2x + 3y = 12
3y = -2x + 12
y = -2x + 4
y-intercept is 4
2. x - 4y = 20
-4y = -x + 20
y = -x - 5
y-intercept is 5
3. y = 2x - 9
this one is easy because it's already in standard form
y-intercept is -9
