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

Example Input: Sentence: 'a crowd of fans watch soccer players from stadium seating'. Find frequency of the letter 'f'
Example Output: 3

Example Input: Sentence: 'people fishing and enlarge mountainlake with trees lining the shoreline'. Find frequency of the letter 't'
Example Output: 4

Example Input: Sentence: 'a yellow long tailed kite being put into the air by a couple'. Find frequency of the letter 'y'
Example Output:
2