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 riding skis down the side of a snow covered ski slope'. How many words start with the letter 's' in the sentence.
Example Output: 5

Example Input: Sentence: 'i am unable to see the image above'. How many words start with the letter 't' in the sentence.
Example Output: 2

Example Input: Sentence: 'two men looking at a building across the street from them'. How many words start with the letter 'a' in the sentence.
Example Output:
3