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 little white airplane that is parked on some concrete'. How many words start with the letter 'p' in the sentence.
Example Output: 1

Example Input: Sentence: 'a passenger train that is passing under some blue bars'. How many words start with the letter 'u' in the sentence.
Example Output: 1

Example Input: Sentence: 'a silver and red passenger jet is parked by the air port'. How many words start with the letter 'a' in the sentence.
Example Output:
3