In this task, you need to count the number of times the given letter appears in the given sentence.

Example Input: Sentence: 'a man sitting on a motorcycle near two other men'. Find frequency of the letter 'r'
Example Output: 3

Example Input: Sentence: 'a man working on a small laptop on a wooden table'. Find frequency of the letter 'l'
Example Output: 4

Example Input: Sentence: 'a silver and black traffic light submerged in water'. Find frequency of the letter 'e'
Example Output:
4