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

[EX Q]: Sentence: 'a close up of a train on a track in the dark'. Find frequency of the letter 'a'
[EX A]: 6

[EX Q]: Sentence: 'a white toilet sitting next to a bathroom sink'. Find frequency of the letter 'b'
[EX A]: 1

[EX Q]: Sentence: 'a green bus driving in a street filled with heavy traffic'. Find frequency of the letter 'v'
[EX A]:
2