Remove the brackets.
12x + 9 = 2x - 15 + 5x + 2
Collect the like terms.
12x + 9 = 7x - 13
Subtract 7x from both sides.
12x - 7x + 9 = -13
5x + 9 = -13
Subtract 9 from both sides.
5x = - 22
Divide by 9
x = - 22/5
x = - 4.4
Check
=====
3(4*-4.4 + 3) = 2(-4.4) - 5(3 - -4.4) + 2
3(-17.6 + 3) = -8.8 - 5(7.4) + 2
3(-14.6) = - 8.8 - 37 + 2
-43.8 =? - 45.8 + 2
-43.8 = -43.8
And it does check.
