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

[EX Q]: Sentence: 'small airplane in the process of taking off'. Find frequency of the letter 'e'
[EX A]: 3

[EX Q]: Sentence: 'a woman walking with a child that is in a wheelchair'. Find frequency of the letter 'k'
[EX A]: 1

[EX Q]: Sentence: 'this is a bus traveling down a street'. Find frequency of the letter 'e'
[EX A]:
3