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

Example Input: Sentence: 'a dog has found a rather large stick for playing fetch'. Find frequency of the letter 't'
Example Output: 3

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 street sign next to for laughs inc'. Find frequency of the letter 'e'
Example Output:
3