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 sailboat is floating near the rocky shore of a beach'. Find frequency of the letter 'o'
5

Sentence: 'a woman wearing skis being pulled by a harnessed dog down a snowy city sidewalk'. Find frequency of the letter 'u'

1