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

[EX Q]: Sentence: 'pedestrian in stripe clothing standing on street corner'. Find frequency of the letter 's'
[EX A]: 4

[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 desk with an electronic device a cell phone and a ipod on it'. Find frequency of the letter 'e'
[EX A]:
7