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

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


[Q]: Sentence: 'a small boat and a large boat on a river near a city'. Find frequency of the letter 'a'
[A]: 10


[Q]: Sentence: 'a stop sign is covered with stickers and graffiti'. Find frequency of the letter 'e'
[A]:
3