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

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

Sentence: 'a plastic tray that has different foods inside of it'. Find frequency of the letter 't'
6

Sentence: 'a colorful plate filled with root vegetables and a fork'. Find frequency of the letter 'r'

3