EXPLANATION
Since we have the system of equations:
(1) 2x - 4y = 20
(2) x = 4
Plugging in x=4 into (1):
2*4 - 4y = 20
Multiplying numbers:
8 - 4y = 20
Subtracting -8 to both sides:
-4y = 20 -8
Subtracting numbers:
-4y = 12
Dividing both sides by -4:
y = 12 / -4
Simplifying:
y = -3
The solution to the system of equations is (x,y) = (4,-3)
