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

Sentence: 'a man and a woman are walking down the street with an umbrella over their heads'. Find frequency of the letter 'w'
4

Sentence: 'two elephants facing each other touching trunks in an enclosure'. Find frequency of the letter 'f'
1

Sentence: 'a couple of boys in a field playing baseball'. Find frequency of the letter 'i'

3