Definition: In this task, you need to reverse 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.
Input: Sentence: 'a man sitting at a table with a plate and cup in front of him and two other guys in the background'. Reverse all words of length '3' in the given sentence.

a nam sitting at a table with a plate dna puc in front of mih dna owt other guys in eht background