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

Example Input: Sentence: 'bananas are being dried in a tropical setting'. Find frequency of the letter 'i'
Example Output: 5

Example Input: Sentence: 'a white bathroom sink sitting next to a toilet'. Find frequency of the letter 'i'
Example Output: 5

Example Input: Sentence: 'a woman is laying on the bed with her feet in a suitcase'. Find frequency of the letter 't'
Example Output:
4

