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

[EX Q]: Sentence: 'small black bird with red on its head standing on a tree branch'. Find frequency of the letter 'b'
[EX A]: 3

[EX Q]: Sentence: 'large grassy pasture filled with trees and a single horse'. Find frequency of the letter 'l'
[EX A]: 4

[EX Q]: Sentence: 'a young man swinging a tennis racquet at a tennis ball'. Find frequency of the letter 'n'
[EX A]:
8