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

[Q]: Sentence: 'a person working at an airport, outside of an airplane'. Find frequency of the letter 'r'
[A]: 5


[Q]: Sentence: 'a man in costume talking on a cell phone'. Find frequency of the letter 'm'
[A]: 2


[Q]: Sentence: 'there are several telephones and two lap tops on the desk'. Find frequency of the letter 's'
[A]:
4