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

Sentence: 'a view from a bathroom shows an open door'. Find frequency of the letter 'o'
7

Sentence: 'a man opening up a package sitting on a couch'. Find frequency of the letter 'n'
5

Sentence: 'a man in tan shirt holding a frisbee in grassy field'. Find frequency of the letter 'n'
5