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 standing next to an elephant and a mirror at the front'. Reverse all words of length '8' in the given sentence.

a man gnidnats next to an tnahpele and a mirror at the front