In this task, you need to count the number of times the given letter appears in the given sentence.
--------
Question: Sentence: 'a sheep in a field in front of other sheep'. Find frequency of the letter 'f'

Answer: 3


Question: Sentence: 'men are riding on motorcycles with a man riding in their carriers'. Find frequency of the letter 'r'

Answer: 8


Question: Sentence: 'a red and white train passing a train station'. Find frequency of the letter 'a'

Answer:
7