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

[Q]: Sentence: 'this yellow fire hydrant sits in a grass field'. Find frequency of the letter 'i'
[A]: 5


[Q]: Sentence: 'three young people goofing around; one of the guys has a football, the girl has a teddy bear'. Find frequency of the letter 'd'
[A]: 3


[Q]: Sentence: 'airplane workers doing an inspection before the plane leaves'. Find frequency of the letter 'n'
[A]:
6