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

Sentence: 'a bus is driving on the street behind some cars'. Find frequency of the letter 'a'
2

Sentence: 'a young boy wearing black and holding a skateboard on the sidewalk'. Find frequency of the letter 'n'
5

Sentence: 'a grey horse with long tail in the trees'. Find frequency of the letter 'e'

5