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

Example Input: Sentence: 'a  woman standing next to a man on a motorcycle in front of a market'. Find frequency of the letter 'l'
Example Output: 1

Example Input: Sentence: 'a crowd of people skiing and enjoying the snow'. Find frequency of the letter 'o'
Example Output: 5

Example Input: Sentence: 'the house in the black and white photo is between trees'. Find frequency of the letter 'e'
Example Output:
9