A cooler contains 66 cans of soda. There are 24 cans of Coca-Cola, 12 cans of Diet Coke, 9 cans of Dr Pepper, 15 cans of Mountain Dew, and 6 cans of Diet Pepsi. If one can of soda is randomly selected, determine the probability that the can is Dr Pepper or Mountain Dew.

Write the theoretical probability answer as a fraction in lowest terms.