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

[Q]: Sentence: 'a man holding a frisbee high into the air'. Find frequency of the letter 'a'
[A]: 4


[Q]: Sentence: 'a gray airplane with metal petals on the wings takes off from an airport'. Find frequency of the letter 'i'
[A]: 4


[Q]: Sentence: 'professional motorcycle stunt rider midair with bike in blue sky'. Find frequency of the letter 'n'
[A]:
3