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 group of people that are by and elephant'. How many words start with the letter 'a' in the sentence.
Example Output: 3

Example Input: Sentence: 'a green mail box sitting next to a white brick building'. How many words start with the letter 'b' in the sentence.
Example Output: 3

Example Input: Sentence: 'a man sitting on top of an orange snowboard'. How many words start with the letter 'o' in the sentence.
Example Output:
3