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: 'the little zebra is looking at the bigger zebra in the field'. Reverse all words of length '6' in the given sentence.

the elttil zebra is looking at the reggib zebra in the field