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

[EX Q]: Sentence: 'a man on stiltz is standing under a pink umbrella'. Find frequency of the letter 's'
[EX A]: 3

[EX Q]: Sentence: 'a young boy wearing black and holding a skateboard on the sidewalk'. Find frequency of the letter 'n'
[EX A]: 5

[EX Q]: Sentence: 'two men talking in a crowded restaurant with a large mirrored wall'. Find frequency of the letter 'r'
[EX A]:
7