instruction:
In this task, you need to count the number of times the given letter appears in the given sentence.
question:
Sentence: 'a piece of film shows two street signs crossing each other'. Find frequency of the letter 'f'
answer:
2


question:
Sentence: 'a man in a black wet suit rides an orange surfboard on the water'. Find frequency of the letter 'o'
answer:
3


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

3