How do you solve this system of linear equation by substitution

x-3y=-12
y=2x+9

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!