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

Example Input: Sentence: 'a cat sleeping near lots of pairs of shoes'. Find frequency of the letter 'r'
Example Output: 2

Example Input: Sentence: 'city two way street with cars lined up on both sides'. Find frequency of the letter 'h'
Example Output: 2

Example Input: Sentence: 'a light is shining through a kitchen window'. Find frequency of the letter 'u'
Example Output:
1