The triple of the double of the difference of 5 and 3.
Wow, what a horribly worded sentence. However, you need to be able to know how to read, understand and solve something like this, no matter how much it may make the English-lover in you cringe. And you thought Faulkner took liberties with language.
The nested parentheses show the order in which the operations are performed: first we find a difference (green bananas), then we double it (yellow bananas), then we triple it (yellowish-brownish bananas). Better hurry, they're fading fast...