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

[EX Q]: Sentence: 'three elephants walk up a dirt trail from the water'. Find frequency of the letter 'l'
[EX A]: 3

[EX Q]: Sentence: 'a person on a sidewalk jumping with an umbrella'. Find frequency of the letter 'a'
[EX A]: 5

[EX Q]: Sentence: 'a close shot of a yellow fire hydrant'. Find frequency of the letter 'e'
[EX A]:
3