First, you isolate b. To do this, you multiply (-2)b/2=-1(-2) and -2 and 2 will cancel each other out. Now you do the same thing to the other side (-2)b/2=-1(-2) and you get -2. Now you replace b with -2. If you solve it, (-2)/2, it will give you -1. Hope I didn't confuse you.
