Hi, Sierra.

You are given these two equations:

4x - 4y = 20,      (1)
      y =  5.      (2)

Let me simplify the equation (1) by dividing its both sides by 4. You will get an equivalent system

x - y = 5,         (1')
    y = 5.         (2')

Let me explain how to solve it graphically.
From eq.(2') you have 

y = x - 5.      

It represents the straight line with the slope 1 (red line in the plot below).

The line y = 5, which is the equation (2'), is the horizontal line (green line in the plot).





Plots y = x - 5 (red line) and y = 5 (green line)



The solution is x = 10, y = 5  (the intersection of the thwo straight lines).

You can check the solution manually.