instruction:
In this task, you need to count the number of times the given letter appears in the given sentence.
question:
Sentence: 'three men in military suits are sitting on a bench,'. Find frequency of the letter 'a'
answer:
3


question:
Sentence: 'several zebras  and a giraffe in an enclosure'. Find frequency of the letter 's'
answer:
3


question:
Sentence: 'a double decker transit bus parks by a blue on the side of the street in front of a brick building in the city'. Find frequency of the letter 't'
answer:

9