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

Sentence: 'a bunch of broken down trains sit in a yard'. Find frequency of the letter 'n'
5

Sentence: 'a bus is driving on the street behind some cars'. Find frequency of the letter 'a'
2

Sentence: 'a woman putting a laptop  in front of a man laying in bed'. Find frequency of the letter 'd'

1