This could be done by first adding x to both sides:
5y - x + x = 20 + x
5y = x + 20
Then divide everything by 5.
y = 1/5x + 4
Now to graph this equation:
Slope intercept form is y = mx + b.
b would be the y intercept and m the slope.
So therefore you know that 4 is the y intercept.
So first just plot the point (0, 4), and then from there you can take the slope and graph it from there. So basically, the y goes up by 1/5 each time the x goes up by 1. So then you could graph it by looking at where 5 is on the x axis and then graphing one above 4 from there, if that makes any sense.