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

Sentence: 'two bears swim in a blue pool of water'. Find frequency of the letter 'o'
4

Sentence: 'there is a person standing on a blue towel'. Find frequency of the letter 'n'
4

Sentence: 'an open black suitcase and a persons arm'. Find frequency of the letter 'k'

1