In this task, you need to count the number of times the given letter appears in the given sentence.

[EX Q]: Sentence: 'a man that is on his cell phone'. Find frequency of the letter 's'
[EX A]: 2

[EX Q]: Sentence: 'town clocks affixed to a tall, brick building'. Find frequency of the letter 'r'
[EX A]: 1

[EX Q]: Sentence: 'a group of people cross the street during winter'. Find frequency of the letter 'p'
[EX A]:
3