Question

How do you solve the following linear system: # -x+3y=-9 , 3x+3y=-18 #?

Answer 1

Use linear combination.

Explanation:

Multiply the first equation by `-1`. Then, add the two equations together to get `4x=-9`, so `x=-9/4`.
Plug `-9/4` back into an equation for `x` and solve for `y`.