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 man sitting on the floor of a living room while a child stands on a snowboard next to him'. How many words start with the letter 'a' in the sentence.
Example Output: 4

Example Input: Sentence: 'a picture of a mirror on a bike'. How many words start with the letter 'o' in the sentence.
Example Output: 2

Example Input: Sentence: 'a boat that is out on top of the grass'. How many words start with the letter 't' in the sentence.
Example Output:
3