There are white, blue, and red boats in a marina. Two-thirds of the boats in the marina are white, 5/8 of the remaining boats are blue, and the rest are red. If there are 6 red boats, how many boats are in the marina?

set a common denominator: 16/24 = w, 5/8 * 1/3 = 5/24 = b, that means 3/24 of the boats are red, and just multiply by 2 to get 6/48 boats are red, and total of 48 boats. (you can check this answer by multiplying the other fractions)