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

[EX Q]: Sentence: 'a bus with two floors belonging to london country'. Find frequency of the letter 't'
[EX A]: 4

[EX Q]: Sentence: 'a couple of men standing inside of a liquor store'. Find frequency of the letter 'p'
[EX A]: 1

[EX Q]: Sentence: 'a person that is walking down the street'. Find frequency of the letter 'n'
[EX A]:
3