4x - 9 = 2x + 15 can someone explain the system used to answer this question

The system is comprised of two processes

that go on at the same time:

#1). Do what ever you want to, to get 'x'

on one side of the equation, and

everything else on the other side.

#2). Whatever you do to one side of the equation,

you must immediately do the same thing to the

other side.

That's the system.

Here's how it works: (I can't believe you're in high school math

and you've never seen, studied, or practiced this before.)

You said that 4x - 9 = 2x + 15

and you need to find

what 'x' is.

Subtract 2x from each side: 2x - 9 = 15

Add 9 to each side: 2x = 24

Divide each side by 2 : x = 12.