Detailed Instructions: In this task, you need to remove all words of a given length in the sentence. The number of letters in a word determine its length, for example, the length of the word "apple" is 5.
Problem:Sentence: 'a black cat laying down in a piece of gray luggage'. Remove all words of length '4' in the given sentence.
Solution:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
a black cat laying in a piece of luggage