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

[EX Q]: Sentence: 'a bird in a tree looking up at branches'. Find frequency of the letter 'e'
[EX A]: 3

[EX Q]: Sentence: 'a man with glasses adjusting his tie in a mirror'. Find frequency of the letter 's'
[EX A]: 5

[EX Q]: Sentence: 'a man at a counter playing interactive bowling video game'. Find frequency of the letter 'o'
[EX A]:
3