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

Example Input: Sentence: 'a teenager witting on a futon couch holding gaming controls in both hands'. Find frequency of the letter 'c'
Example Output: 3

Example Input: Sentence: 'a truck is parked in front of a store'. Find frequency of the letter 't'
Example Output: 3

Example Input: Sentence: 'a cat almost all the way inside the bowl of a toilet'. Find frequency of the letter 'c'
Example Output:
1