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

[Q]: Sentence: 'some people sitting on surfboards in the water'. Find frequency of the letter 't'
[A]: 4


[Q]: Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'
[A]: 2


[Q]: Sentence: 'a man surfs a small wave in the ocean'. Find frequency of the letter 's'
[A]:
3