X+2x+3=4x-12
3x+3=4x-12
3x-4x=-12-3
-x=-15
x=15

How do I verify x?

True

General Formulas and Concepts:

Order of Operations: BPEMDAS

Explanation:

In order to verify x, simply plug it back into the original equation to see if the equation would be true.

Step 1: Define

Original Function: x + 2x + 3 = 4x - 12

x = 15

Step 2: Verify

Since 48 does indeed equal to 48, 15 would be a solution. Therefore, x = 15 is verified and true.