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

Sentence: 'two zebras feed on a plant through some wire mesh'. Find frequency of the letter 'o'
4

Sentence: 'a photo of a toilet which is not clean'. Find frequency of the letter 'w'
1

Sentence: 'the girl with glasses is holding a giant toothbrush close to her mouth'. Find frequency of the letter 'n'

2