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

[Q]: Sentence: 'a man riding a white surfboard on a large wave'. Find frequency of the letter 'a'
[A]: 7


[Q]: Sentence: 'one woman is arranging the other woman's hair'. Find frequency of the letter 'o'
[A]: 4


[Q]: Sentence: 'a man walks his cows on a public street'. Find frequency of the letter 's'
[A]:
4