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

Sentence: 'a couple of men sitting next to each other under an umbrella'. Find frequency of the letter 'n'
5

Sentence: 'tow birds flying by a long necked crane'. Find frequency of the letter 'f'
1

Sentence: 'a smiling man wearing a dragon t-shirt holds a bunch of green bananas or plantains'. Find frequency of the letter 'a'

11