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: 'a baseball player prepares to swing at a pitch'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'two couples sit on a bench in front of bushes with pink flowers'. How many words start with the letter 'o' in the sentence.
Example Output: 2

Example Input: Sentence: 'a young baby has his hair brushed by mom'. How many words start with the letter 'b' in the sentence.
Example Output:
3