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

[EX Q]: Sentence: 'a plastic plastic plate topped with three different type of food'. Find frequency of the letter 'l'
[EX A]: 3

[EX Q]: Sentence: 'a couple of boys in a field playing baseball'. Find frequency of the letter 'i'
[EX A]: 3

[EX Q]: Sentence: 'a man serving plates of hot dogs and hamburgers'. Find frequency of the letter 'r'
[EX A]:
3