The enormous, double-decker plane can seat over 800 people.
This is not an answer choice, but i am wondering if this works -
The enormous double-decker plane can seat over 800 people.
Which version are you questioning? There should be no comma.
oh sorry, the one with the comma is the right answer, but i am wondering if the sentence still works without the comma.
Where is this question from?
I think your book is wrong.
The use of comma is dictated by the type of adjectives that are in the sentence: coordinate adjectives ARE separated by commas, whereas cumulative adjectives ARE NOT.
Coordinate adjectives are adjectives in a list that each separately modify the noun, as in “tall, skinny boy.” Both “tall” and “skinny” modify “boy.” You can easily rearrange the adjectives and say, “skinny, tall boy."
Cumulative adjectives, in contrast, don’t separately modify the noun that follows. Instead, the adjective right before the noun pairs with the noun as a unit (as in “double-decker bus,”) and the adjective before that unit modifies them both. For example, in “expensive haute couture,” “haute” modifies “couture.” These become a unit—and then “expensive” modifies “haute couture.” (Note that you cannot easily rearrange the adjectives in this scenario – “haute expensive couture” won’t work. Neither will “double-decker enormous bus.”)
If I am indeed correct that “enormous” and “double-decker” are cumulative rather than coordinate adjectives, then your book is wrong.
That’s the sentence, but what does the question ask you to do?