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

Sentence: 'a railroad train pulling up to the train platform'. Find frequency of the letter 'o'
3

Sentence: 'baseball player reaching back as he's about to throw the ball'. Find frequency of the letter 'e'
5

Sentence: 'a rear view mirror for a motorcycle with a tall building in it's reflection'. Find frequency of the letter 'c'

3