In this task, you need to count the number of words in a sentence that start with the given letter. Answer with numbers and not words.

Example Input: Sentence: 'several people watch cars drive by with bikes on them'. How many words start with the letter 'b' in the sentence.
Example Output: 2

Example Input: Sentence: 'a train traveling through a tunnel on a model track'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a man holding a teddy bear sleeping on a green plaid couch'. How many words start with the letter 'a' in the sentence.
Example Output:
3