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

Sentence: 'a picture of two computers on a table'. Find frequency of the letter 'r'
2

Sentence: 'a small white plane sitting on top of the ocean'. Find frequency of the letter 'e'
4

Sentence: 'six snow boarders posing with their snow boards'. Find frequency of the letter 'r'

4