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

Sentence: 'girls posing of a picture one holding a tennis racket the other wearing a crown'. Find frequency of the letter 'g'
4

Sentence: 'a group of people walking down a rain soaked street with umbrellas'. Find frequency of the letter 'w'
3

Sentence: 'man wearing coat and hat posing for photo in front of wall'. Find frequency of the letter 'o'
7