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

[EX Q]: Sentence: 'two metal benches on an empty train platform'. Find frequency of the letter 'n'
[EX A]: 4

[EX Q]: Sentence: 'there is a baseball game on and a few people are watching'. Find frequency of the letter 'i'
[EX A]: 2

[EX Q]: Sentence: 'a baby sheep feeding on a adult sheep in a field'. Find frequency of the letter 'a'
[EX A]:
5