When you have two equations with two variables you need a system of equations.

For example:

Equation 1: X - Y = 8

Equation 2: X - 2Y= - 20

From equation 1 solve for one variable,

(choose the easiest one to solve, in this case "X")

X - Y = 8

X= Y + 8

Now substitute it into equation 2

X - 2Y = 20

(Y + 8 ) - 2Y= -20

-Y + 8= -20

-Y= -20 - 8

-Y= -28

Y= 28

Find the value of "X" by substituting Y=28 into the first equation

X= 28 + 8 = 36

X= 36

You can verify your answer by substituting your values into the original equation

36 - 28 = 8

36- 2(28) = - 20

Practice Problems: