D+30=1.8d please help me solve this step by step asap

In a class, there are 12 girls. if the ratio of boys to girls is 5: 4 how many boys are there in the class

Twelve less than a number is at most 20

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?