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: 'an ambulance tipped on its side in the street with the back door open'. Reverse all words of length '9' in the given sentence.

an ecnalubma tipped on its side in the street with the back door open