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

Sentence: 'a blue train on a track next to another track'. Find frequency of the letter 'c'
2

Sentence: 'a couple of men sitting next to each other under an umbrella'. Find frequency of the letter 'n'
5

Sentence: 'an adorable little girl riding skis on the snow'. Find frequency of the letter 'n'

4