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

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


[Q]: Sentence: 'a group of cars and house on truck passing in a street'. Find frequency of the letter 'i'
[A]: 2


[Q]: Sentence: 'a living room with a television and brown couch has a clothes hanger on the doorknob'. Find frequency of the letter 'w'
[A]:
2