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

[EX Q]: Sentence: 'a group of people stand inside of a big room'. Find frequency of the letter 'o'
[EX A]: 6

[EX Q]: Sentence: 'a group of three dogs laying on a kitchen floor'. Find frequency of the letter 'r'
[EX A]: 3

[EX Q]: Sentence: 'three people on horse back at a rural road intersection'. Find frequency of the letter 'o'
[EX A]:
5