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

Sentence: 'a large cooked pizza on a dining table'. Find frequency of the letter 'n'
3

Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'
3

Sentence: 'orange mass transit trolley working it's way through a city'. Find frequency of the letter 'n'

3