X+2y=-1 and 4x-4y=20 solve by substitution

To do this problem you would first need to factor out a variable, which in this case I would want to do the first equation because it is isolated. Now the equations would look like this:

x = -2y - 1

4x - 4y = 20

Since we know that x is now equal to -2y - 1 we can plug it in to the x value in the second equation:

4 (-2y -1) - 4y = 20

-8y -4 - 4y

-12y - 4 = 20

-12y = 24

y = -2

Now that we know the y value plug the y value to one equation to find the x, I will be using the first equation

x + 2(-2) = -1

x - 4 = -1

x = 3

Solutions:

y = -2

x = 3