Problem A: At a carnival, there are two food stands selling hot dogs and pizzas. The hot dog stand sells hot dogs for $3 each and the pizza stand sells pizzas for $12 each. If Dylan bought a total of 15 hot dogs and pizzas combined for $51, how many of each did he buy? Problem B: Bianca has two bags of marbles. The first bag contains 20 blue marbles and 10 red marbles. The second bag contains 30 green marbles and 15 purple marbles. If Bianca randomly chooses one marble from each bag, what is the probability that she will choose a blue marble and a green marble