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

[EX Q]: Sentence: 'a crowd of people standing in front of a green train'. Find frequency of the letter 'g'
[EX A]: 2

[EX Q]: Sentence: 'a railroad train pulling up to the train platform'. Find frequency of the letter 'o'
[EX A]: 3

[EX Q]: Sentence: 'a laptop and a desk lamp left on alone in a room'. Find frequency of the letter 'd'
[EX A]:
2