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

Sentence: 'a tennis player after hitting a shot back to the other side of the court'. Find frequency of the letter 'n'
3

Sentence: 'a couple of buses parked on the side of the street'. Find frequency of the letter 'b'
1

Sentence: 'a group of large and small elephants walking on top of grass'. Find frequency of the letter 'f'

2