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 group of cows that are standing in the grass'. Find frequency of the letter 'g'
[EX A]: 3

[EX Q]: Sentence: 'a young asian guy carrying a suitcase and smiling'. Find frequency of the letter 'r'
[EX A]:
2