Answer:
infinite amount of solutions.
Explanation:
-21=-21-b
-b= -21+21
-b= 0
There is no argument: In real numbers, not only is x/0 undefined for any x, but infinity is not a number, thus it cannot be the result of a division. But there are ways to extend the real numbers (in other words, consider new systems) that do have one or more points at infinity, and some even permit arithmetic to be extended.
Hope I helped
-Liberty 8th grade, Chicago Illinois.