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 woman standing in front of a bathroom sink in front of a mirror'. Find frequency of the letter 'o'
[A]: 8


[Q]: Sentence: 'a traffic signal by a wire filled with some birds'. Find frequency of the letter 'e'
[A]:
3