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 group of cars and house on truck passing in a street'. Find frequency of the letter 'i'
[A]: 2


[Q]: Sentence: 'a guy siting down in a chair eating'. Find frequency of the letter 'u'
[A]:
1