Question

How do you solve the system using the substitution method for x+y=9 and y=12?

Answer 1

Substitute `12` for `y` in `x+y=9`
to get `x=-3`

Explanation:

Given
[1]`color(white)("XXX")x+y =9`
[2]`color(white)("XXX")y=12`

Based on [2] we can substitute `12` for `y` in [1]
[3]`color(white)("XXX")x+12=9`

Subtracting `12` from both sides gives
[5]`color(white)("XXX")x=-3`