23x34=(20+3)x(30+4) what property does this demonstrate

Which representation has a constant of variation of -2.5

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?

Solve the formula ax+ by = c for x.