Take the 28 and tern it into -28 and do it on both sides, -28 + 28 = 0, -28 + -1 = -30.
Sence x represents one aka any number you will add x with 11 and you will get 12x^2
Now you have to divide 12 on both sides, 12 divided by 12 is 1 so it eliminates it, 12 divided by -30 = -2.5, so then X = -2.5, and that should be right
I hope this helps! =)