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

Sentence: 'an orange cat sitting on the ground next to a  purse'. Find frequency of the letter 's'
2

Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'
2

Sentence: 'a large teddy bear that is next to a pool'. Find frequency of the letter 'a'

5