Question

How do you solve `x-y=3` and `x-2y=3`?

Answer 1

Subtract one of the given equations from the other to get
`color(white)("XXXX")` `y=0`
then substitute back into either of the equations to get
`color(white)("XXXX")` `x=3`

Explanation:

[1]`color(white)("XXXX")` `x-y=3`
[2]`color(white)("XXXX")` `x-2y=3`

Subtract [2] from [1]
[3]`color(white)("XXXX")` `y=0`

Substitute `0` for `y` in [1]
[4]`color(white)("XXXX")` `x-0=3`
[5]`color(white)("XXXX")` `x=3`