We know there are a total of 36 marbles. We also know 24 out of 36 are black and 12 out of 36 are blue. A ratio is pretty much a division problem... The problem wants the 24 black marbles over the 12 blue marbles. So, 24/12 = 2/1. Now, what this means is that for every 2 black marbles, there is one 1 blue marble. Good luck!
Cole can learn how to play tennis. But if he saved the money, he can save up and get something bigger, or save up for college. There is only so much he can do with a tennis racket except for using it to learn a new sport.