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

[EX Q]: Sentence: 'a small white dog looking out a car window'. Find frequency of the letter 'l'
[EX A]: 3

[EX Q]: Sentence: 'a jet flying through the clear blue sky'. Find frequency of the letter 'g'
[EX A]: 2

[EX Q]: Sentence: 'a train riding along the tracks with green grass on both sides'. Find frequency of the letter 'k'
[EX A]:
1