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

Sentence: 'two zebras standing around while a third zebra drinks from a pond'. Find frequency of the letter 's'
3

Sentence: 'a black bear sitting in the grass taking a rest'. Find frequency of the letter 'a'
6

Sentence: 'a giraffe standing outside doing a silly pose'. Find frequency of the letter 'e'

3