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

Sentence: 'a man in a black shirt prepares to catch a frisbee'. Find frequency of the letter 'f'
1

Sentence: 'a train going over a bridge with some buildings in the background'. Find frequency of the letter 'd'
3

Sentence: 'a jet that is flying in the sky with a banner behind it'. Find frequency of the letter 'r'

1