Answer:
[tex]x=12-3y[/tex]
Step-by-step explanation:
Question wants to know WHAT EXPRESSION would you substitute into Equation 1 IF you solve for x in Equation 2.
Let's do some algebra and solve for x in Equation 2:
[tex]-x-3y=-12\\-x=-12+3y\\x=\frac{-12+3y}{-1}\\x=12-3y[/tex]
This is the expression we would substitute into [tex]x[/tex] of Equation 1 in order to use substitution method and solve.