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

Sentence: 'small airplane in the process of taking off'. Find frequency of the letter 'e'
3

Sentence: 'a person with some scissors over a bowl'. Find frequency of the letter 's'
6

Sentence: 'vanity sitting atop a base with two doors and a mirror overhead'. Find frequency of the letter 'n'

3