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

[EX Q]: Sentence: 'an orange cat sitting on the ground next to a  purse'. Find frequency of the letter 's'
[EX A]: 2

[EX Q]: Sentence: 'a crowd of people standing in front of a green train'. Find frequency of the letter 'g'
[EX A]: 2

[EX Q]: Sentence: 'a couple of street signs sit on a train light'. Find frequency of the letter 'h'
[EX A]:
1