Please give me an explanation
-8[-20+(-9+5)²]=32

Solve the equation 3x2 + 19x + 9 = 0 to the nearest tenth.

The verbal translation for the difference of m and 7 increased by 15

There are three bags: a (contains 2 white and 4 red balls), b (8 white, 4 red) and c (1 white 3 red). you select one ball at random from each bag, observe that exactly two are white, but forget which ball came from which bag. what is the probability that you selected a white ball from bag a?