Finding x:
If y=2x+9, substitute y into the equation x-3y=-12.
You will get: x-3(2x+9)=-12
Now, distribute: x-6x-27=-12
Add like terms: -5x-27=-12
Add 27 to both sides: -5x=15
Divide both sides by -5: x=-3
Now, substitute this value of x into the equation to find y: y=2(-3)+9
Multiply: y=-6+9
Add: y=3
Here is the solution: (x,y)=(-3,3)
Hope this explanation helped!
