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

[Q]: Sentence: 'a young boy wearing black and holding a skateboard on the sidewalk'. Find frequency of the letter 'n'
[A]: 5


[Q]: Sentence: 'a couple of men standing inside of a liquor store'. Find frequency of the letter 'p'
[A]: 1


[Q]: Sentence: 'three cows are lying down near a road'. Find frequency of the letter 'l'
[A]:
1