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: 'some signs buildings trees bushes a green and white sign'. How many words start with the letter 's' in the sentence.
Example Output: 3

Example Input: Sentence: 'a tall zebra grazing on a lush green field'. How many words start with the letter 't' in the sentence.
Example Output: 1

Example Input: Sentence: 'a man riding the subway sitting next to his backpack holding his bike'. How many words start with the letter 's' in the sentence.
Example Output:
2