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

[Q]: Sentence: 'a double-decker bus covered in children's illustrations driving next to a van'. Find frequency of the letter 'a'
[A]: 4


[Q]: Sentence: 'a man hits a tennis ball with a racket on the court'. Find frequency of the letter 'c'
[A]: 2


[Q]: Sentence: 'a train traveling through a train yard next to a light pole'. Find frequency of the letter 'n'
[A]:
4