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

Sentence: 'a toilet sits in a cluttered bathroom next to a sink'. Find frequency of the letter 'a'
4

Sentence: 'a white bowl filled with peeled orange slices'. Find frequency of the letter 's'
2

Sentence: 'some pink roses are in a square glass vase'. Find frequency of the letter 'r'

3