Given the task definition and input, reply with output. In this task, you need to remove 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.

Sentence: 'a duck and baby ducks are in the blue water'. Remove all words of length '4' in the given sentence.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
a and ducks are in the water