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

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


[Q]: Sentence: 'a bird is standing on the ledge of the building'. Find frequency of the letter 't'
[A]: 3


[Q]: Sentence: 'a couple of cellphones are laying out together'. Find frequency of the letter 't'
[A]:
3