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: 'small black bird with red on its head standing on a tree branch'. Find frequency of the letter 'b'
3

Sentence: 'a man sitting down while on a cell phone'. Find frequency of the letter 'e'

3