in an ensemble of gongs, all gongs have a diameter of either ten inches, twelve inches, or fifteen inches. in the collection, there are 18 ten-inch gongs. half of the gongs in the collection are tiger gongs. of the tiger gongs, there are equal numbers of ten-inch, twelve-inch and fifteen-inch gongs. half of the twelve-inch gongs are not tiger gongs, and half of all gongs are fifteen inches in diameter. how many gongs are there in the collection?
