instruction:
In this task, you need to count the number of times the given letter appears in the given sentence.
question:
Sentence: 'a man and several white red and blue airplanes'. Find frequency of the letter 'u'
answer:
1


question:
Sentence: 'two people under an umbrella while walking down a sidewalk'. Find frequency of the letter 'i'
answer:
3


question:
Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'
answer:

5