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

Sentence: 'some giraffes moving across a big grass field'. Find frequency of the letter 'e'
3

Sentence: 'a man riding on the back of a white horse next to other horses'. Find frequency of the letter 'o'
6

Sentence: 'the man is testing out a new video game'. Find frequency of the letter 'i'

3