What is substitution?

It's a way of solving a set of equations by substituting a varialbe with one of the equations (I don't know if that's the best way to describe it tho)

EX:

3y - 2x = 11
y + 2x = 9

First you have to solve one of the equations as x= or y=
If you do the 2nd one you have

y = 9 - 2x


Now substitute that equation into the first one to solve for x

3 (9-2x) - 2x = 11

Now solve:

(27 - 6x) - 2x = 11
27 - 6x - 2x = 11
27 - 8x = 11
-8x = -16
x = 2

Now that you have a value for x, place the x value into either original equation to solve for y

y = 9 - 2(2)
y = 9 - 4
y = 5

Disco!

Thanks for the help, that will help me a lot