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

[Q]: Sentence: 'a black computer with a screen reading "press any key to begin."'. Find frequency of the letter 'a'
[A]: 5


[Q]: Sentence: 'different sets of luggage in a baggage claim area'. Find frequency of the letter 'r'
[A]: 2


[Q]: Sentence: 'a young girl standing under a window next to a toilet'. Find frequency of the letter 'r'
[A]:
2