Depends on what you are asking
Y = Mx + c
Finding the equation of the line
Which is y = -3x + 8
Or for finding y
Y = 8-3x
Or if u wanna find x
You subtract y from both sides
3x = 8 - y
Dividing both sides by 3
3x/3 = 8/3 -y/3
Which leave 8 -y divided by 3