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

[Q]: Sentence: 'two persons standing outside a moving sub train'. Find frequency of the letter 'a'
[A]: 3

[Q]: Sentence: 'man riding a skate board down the little board way'. Find frequency of the letter 'k'
[A]: 1

[Q]: Sentence: 'there are two bunk beds and a ladder'. Find frequency of the letter 't'
[A]:
2