Question

How do you solve the system `x + 4y = 28` and `- x + 4y = 20`?

Answer 1

`(x,y) = (4,6)`

Explanation:

[1]`color(white)("XXXX")` `x+4y = 28`
[2]`color(white)("XXXX")` `-x+4y = 20`

adding [1] and [2]
[3]`color(white)("XXXX")` `8y = 48`
dividing by 8
[4]`color(white)("XXXX")` `y = 6`

substituting `6` for `y` (from [4]) in [1]
[5]`color(white)("XXXX")` `x +4(6) = 28`
simplifying
[6]`color(white)("XXXX")` `x = 4`