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

[EX Q]: Sentence: 'person wearing all white leaned up against a wall with a yellow sign'. Find frequency of the letter 'a'
[EX A]: 8

[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: 'two slices of pizza with toppings on white papers'. Find frequency of the letter 'n'
[EX A]:
2