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

[EX Q]: Sentence: 'a man in a sweatshirt is taking his own picture'. Find frequency of the letter 'u'
[EX A]: 1

[EX Q]: Sentence: 'a giraffe shares a habitat with a zebra, an ostrich, and an okapi'. Find frequency of the letter 'e'
[EX A]: 3

[EX Q]: Sentence: 'a sign post with street signs and stop sign by a tree'. Find frequency of the letter 'o'
[EX A]:
2