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

[EX Q]: Sentence: 'a group of people standing on grass with a train in the background'. Find frequency of the letter 'n'
[EX A]: 6

[EX Q]: Sentence: 'a street at night with trees and streetlights on'. Find frequency of the letter 't'
[EX A]: 9

[EX Q]: Sentence: 'a woman playing tennis on the tennis court while people watch'. Find frequency of the letter 'e'
[EX A]:
6