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 bathroom with a sink, counter top, and mirror is shown'. Find frequency of the letter 'i'
4

Sentence: 'a car accident has slowed traffic as a clean up crew works'. Find frequency of the letter 'f'

2