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

Sentence: 'a man sitting inside a green military truck talking to someone'. Find frequency of the letter 'i'
7

Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'
5

Sentence: 'four people are riding in the canoe in the water'. Find frequency of the letter 'e'

7