Answer:
You would use a = 12
Step-by-step explanation:
The b value is the coefficient that is in front of the x term, that does not have an exponent of 2. It's simply the x term (not the x^2 term)
We're told that b = 15 is used, but we see that -15 is in front of the x term. To fix this contradiction, add 15x to both sides so that you move the x term to the right side
-15x+22 = 12x^2
-15x+22+15x = 12x^2+15x
22 = 12x^2+15x
Now subtract 22 from both sides to move that term over as well
22-22 = 12x^2 + 15x - 22
0 = 12x^2 + 15x - 22
12x^2 + 15x - 22 = 0
12x^2 + 15x + (-22) = 0
The last equation is in the form ax^2 + bx + c = 0 with
a = 12, b = 15, c = -22
