Let's solve for y.
4x+7y=28
Add -4x to both sides.
4x+7y+−4x=28+−4x
7y=−4x+28
Divide both sides by 7.
7y/7=−4x+28/7
y=−4/7x+4
Store #2 since it has a lower MAD
The third one is 510 not show in the pic here

To divide by a fraction, you multiply by its reciprocal, which you find by flipping the numerator and the denominator. 
Multiply the numerators and the denominators separately. 
Simplify by dividing both sides of the equation by
. 