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

[Q]: Sentence: 'a small white plane sitting on top of the ocean'. Find frequency of the letter 'e'
[A]: 4


[Q]: Sentence: 'a green bus driving in a street filled with heavy traffic'. Find frequency of the letter 'v'
[A]: 2


[Q]: Sentence: 'several sail boats with red sails sailing along a river'. Find frequency of the letter 'v'
[A]:
2