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

Sentence: 'a doorway looking into a small bathroom with white toilet'. Find frequency of the letter 'r'
2

Sentence: 'a picture of two men on a motorcycle in front of a railroad track'. Find frequency of the letter 'n'
4

Sentence: 'a stop sign next to houses with christmas lights'. Find frequency of the letter 's'

7