Graciela picks a white mouse at random from a bin of 8 white mice 2 gray mice and 2 brown mice what is the probability

In the polynomial below, what number should replace the question mark to produce a difference of squares? x2 + ? x - 36

Ineed to know the answer to this algebra question.

Which of these numbers of simulations of an event would be most likely to produce results that are closest to those predicted by probability theory? 15, 20, 5, 10