Instructions: 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 ice cream cake with marshmellows and chocolate for a 3 year birthday'. Reverse all words of length '3' in the given sentence.
Output:
a eci cream cake with marshmellows dna chocolate rof a 3 year birthday