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

Sentence: 'an commercial airline airplane flies above the clouds'. Find frequency of the letter 'n'
3

Sentence: 'hotel towels with sunglasses perched and hotel business cards and catalog'. Find frequency of the letter 'o'
4

Sentence: 'a tennis player swinging a racket at a ball'. Find frequency of the letter 'r'

2