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 train passes over a quiet city park on a bridge'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'an elephant standing in front of some trees with its trunk in the air'. How many words start with the letter 's' in the sentence.
Example Output: 2

Example Input: Sentence: 'a man in a black leather jacket is near others and umbrellas'. How many words start with the letter 'b' in the sentence.
Example Output:
1