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

Sentence: 'a man flying through the air on top of a skateboard'. Find frequency of the letter 'h'
3

Sentence: 'a red train traveling down train tracks near a forest'. Find frequency of the letter 'f'
1

Sentence: 'a bed with a wire bed frame and a colorful bed spread'. Find frequency of the letter 'd'
5