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 skateboarder performing tricks under the lights at night'. How many words start with the letter 'u' in the sentence.
Example Output: 1

Example Input: Sentence: 'a mother bear and her two young are crossing a shallow river'. How many words start with the letter 'a' in the sentence.
Example Output: 4

Example Input: Sentence: 'a group of four skiers are getting ready to embark'. How many words start with the letter 'g' in the sentence.
Example Output:
2