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

Sentence: 'a crowd of people standing in front of a green train'. Find frequency of the letter 'g'
2

Sentence: 'this yellow fire hydrant sits in a grass field'. Find frequency of the letter 'i'
5

Sentence: 'a motorcycle parked in front of a house'. Find frequency of the letter 's'

1