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

[Q]: Sentence: 'bathroom scene with a black cat going behind the door'. Find frequency of the letter 'e'
[A]: 4


[Q]: Sentence: 'a passenger bus that is driving down the street'. Find frequency of the letter 'r'
[A]: 3


[Q]: Sentence: 'a man holding a black hat and wearing a yellow shirt water skiing in the ocean'. Find frequency of the letter 'a'
[A]:
10