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

[EX Q]: Sentence: 'some giraffes moving across a big grass field'. Find frequency of the letter 'e'
[EX A]: 3

[EX Q]: Sentence: 'a person is water skiing and there are birds flying around above them'. Find frequency of the letter 'n'
[EX A]: 5

[EX Q]: Sentence: 'a little kid riding skis holding two ski poles'. Find frequency of the letter 's'
[EX A]:
4