To solve for "b" you must isolate it, meaning that "b" must be the only thing on the right side of the equation.
First you must combine like terms. Like terms are numbers that have matching variables OR are numbers with out variables. In this case the like terms are -8b and -7b, since they both have the variables "b" attached.
-8b + (-7b) = -15b
so...
-75 = -15b
Next, to completely isolate b, divide -15 to both sides. Since -15 is being multiplied by b, division (the opposite of multiplication) will cancel -15 out (in this case it will make -15 one) from the right side and bring it over to the left side.
