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

Sentence: 'there is a zebra that is walking enar a car'. Find frequency of the letter 'r'
4

Sentence: 'a group of tennis players on a tennis court'. Find frequency of the letter 'o'
4

Sentence: 'two people sitting on a couch watching the television'. Find frequency of the letter 'l'

2