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

Sentence: 'a young woman dressed in green and black operating a remote control'. Find frequency of the letter 'r'
5

Sentence: 'a person riding a skate board on a city street'. Find frequency of the letter 'a'
5

Sentence: 'a photograph of two red teddy bears sitting on counters'. Find frequency of the letter 'o'

6