Answer: 19/30 or about 63%
Explanation: Add all your marble up so 6+4+5+15 to get the total amount of options or marbles in this case. Now find out how many red and blue marbles you have so 4+15 or 19 now you can divide the red and blue marbles by the total amount of marbles to get your percentage of pulling a red or blue marble from the bag.