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 black bear walks in front of a tree in a forest'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a man putting a protective covering over a large tv screen'. How many words start with the letter 'l' in the sentence.
Example Output: 1

Example Input: Sentence: 'a herd of elephants splashing around in a river'. How many words start with the letter 'r' in the sentence.
Example Output:
1