Let's worry about graphing this first: 5y-x=20
If you set x = 0, then y = 4, and the y-intercept is then (0,4).
If you set y = 0, then x = -20, and the x-intercept is (-20,0).
Plot these 2 pts and then draw a str. line thru them. Done!
If you wish to solve 5y-x=20 for y:
1) add x to both sides: 5y = 20
2) divide both sides by 5: y = 4