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 silver and blue amtrak train sitting below tall buildings'. How many words start with the letter 'b' in the sentence.
Example Output: 3

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 girl and her dog walk past a bike'. How many words start with the letter 'a' in the sentence.
Example Output:
3