If this is set equal to 0, then the solution set for this is b = -1/2 or b = 3.
To solve this, you want to factor. The best way to do so if by splitting down the middle and factoring each set.
4b^2 - 12b ---> pull out greatest common factor
4b(b - 3)
Do the same with the other side.
2b + 6 ---> pull out greatest common factor
2(b -3)
Now since there is the same remainder left over, you can put the two GCF's in a parenthesis together multiplied by the remainder.
(4b + 2)(b - 3)
Set each parenthesis equal to 0 and solve.
