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

Sentence: 'the street sign is next to a curved road'. Find frequency of the letter 's'
3

Sentence: 'an old woman is holding her cat in front of a camera'. Find frequency of the letter 'r'
3

Sentence: 'a bottle sitting on a green park bench'. Find frequency of the letter 'e'

4