instruction:
In this task, you need to count the number of times the given letter appears in the given sentence.
question:
Sentence: 'a man flying through the air on top of a skateboard'. Find frequency of the letter 'r'
answer:
3

question:
Sentence: 'a gray elephant is in a grassy field'. Find frequency of the letter 'e'
answer:
3

question:
Sentence: 'some guys sitting on a blanket at the park while eating some hot dogs'. Find frequency of the letter 'n'
answer:
4