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

[Q]: Sentence: 'a girl sits on a surfboard and smiles'. Find frequency of the letter 'i'
[A]: 3


[Q]: Sentence: 'a car accident has slowed traffic as a clean up crew works'. Find frequency of the letter 'f'
[A]: 2


[Q]: Sentence: 'people selling their foods at a farmer's market'. Find frequency of the letter 'o'
[A]:
3