Question

What is the solution to 2x+12=5x-9

Answer 1

$2x+12=5x-9\ \ \ \ |combine\ like\ terms\\\\2x-5x=-9-12\ \ \ \ \ |simplify\\\\-3x=-21\ \ \ \ \ |:-3\\\\x=7$

Answer 2

So 2x+12=5x-9
you want all of the unknowns on one side and all of  the known values on the other or
subtract 2x from both sides
12=3x-9
add 9 to both sides
21=3x
divide both sides by 3
7=x