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

[Q]: Sentence: 'a girl playing with a frisbee while people watch'. Find frequency of the letter 'e'
[A]: 5


[Q]: Sentence: 'a man standing on a tennis court holding a racquet'. Find frequency of the letter 's'
[A]: 2


[Q]: Sentence: 'a man stands in a doorway inside a building with a white refrigerator on the side'. Find frequency of the letter 'r'
[A]:
5