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: 'people playing wii bowling in a modern library'. Find frequency of the letter 'o'

Answer: 3


Question: Sentence: 'there is a dell lap top that is on the table and it is open'. Find frequency of the letter 'n'

Answer:
3