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

[EX Q]: Sentence: 'two people are riding on canoes down a river'. Find frequency of the letter 'e'
[EX A]: 5

[EX Q]: Sentence: 'a couple of men standing inside of a liquor store'. Find frequency of the letter 'p'
[EX A]: 1

[EX Q]: Sentence: 'a man and several white red and blue airplanes'. Find frequency of the letter 'u'
[EX A]:
1