instruction:
In this task, you need to count the number of times the given letter appears in the given sentence.
question:
Sentence: 'a red and white train passing a train station'. Find frequency of the letter 'a'
answer:
7


question:
Sentence: 'an image of a street sign with a corner restaurant'. Find frequency of the letter 'u'
answer:
1


question:
Sentence: 'a little girl standing outside holding onto a yellow umbrella'. Find frequency of the letter 'e'
answer:

4