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

Sentence: 'a jet that is flying in the sky with a banner behind it'. Find frequency of the letter 'r'
1

Sentence: 'two people under an umbrella while walking down a sidewalk'. Find frequency of the letter 'i'
3

Sentence: 'a double-decker bus makes its way down a snowy street'. Find frequency of the letter 'd'

3