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

[EX Q]: Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'
[EX A]: 3

[EX Q]: Sentence: 'an airplane is being towed away from the jet bridge'. Find frequency of the letter 's'
[EX A]: 1

[EX Q]: Sentence: 'a pretty young lady playing a game of frisbee'. Find frequency of the letter 'g'
[EX A]:
3