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

[EX Q]: Sentence: 'a white police vehicle parked on a paved street'. Find frequency of the letter 'a'
[EX A]: 4

[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 woman standing on a tennis court holding a racquet'. Find frequency of the letter 'n'
[EX A]:
7