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 male skateboarder in a black shirt doing a trick'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'an officer sits on a brown horse on a city street'. How many words start with the letter 'o' in the sentence.
Example Output: 3

Example Input: Sentence: 'a skateboarder doing a neat trick in a half pipe'. How many words start with the letter 'a' in the sentence.
Example Output:
3