instruction:
In this task, you need to count the number of times the given letter appears in the given sentence.
question:
Sentence: 'a passenger train that is going over a bridge'. Find frequency of the letter 't'
answer:
3


question:
Sentence: 'a large grass pasture land with sheep grazing on grass'. Find frequency of the letter 'a'
answer:
7


question:
Sentence: 'an animal standing on the side of a grass covered field'. Find frequency of the letter 'r'
answer:

2