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: 'an indoor bathroom with reflective marble counter tops'. How many words start with the letter 'i' in the sentence.
Example Output: 1

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 little boy is waving at the runway as a plane is sitting waiting for takeoff'. How many words start with the letter 'a' in the sentence.
Example Output:
4