instruction:
In this task, you need to count the number of times the given letter appears in the given sentence.
question:
Sentence: 'a guy surfs a wave with his surfboard'. Find frequency of the letter 's'
answer:
4


question:
Sentence: 'a small boat and a large boat on a river near a city'. Find frequency of the letter 'a'
answer:
10


question:
Sentence: 'a black dog sitting with a girl in the back of a car'. Find frequency of the letter 'k'
answer:

2