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

Sentence: 'a jet flying through the clear blue sky'. Find frequency of the letter 'g'
2

Sentence: 'a man holding a baseball bat an playing baseball'. Find frequency of the letter 'l'
6

Sentence: 'a group of people standing on grass with a train in the background'. Find frequency of the letter 'n'

6