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: 'two boats are docked near the side of a water way while several people are on the grass beside them'. Reverse all words of length '3' in the given sentence.

owt boats era docked near eht side of a water yaw while several people era on eht grass beside them