TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'

SOLUTION: 3

PROBLEM: Sentence: 'an old glass vase containing flowers on a glass table'. Find frequency of the letter 'b'

SOLUTION: 1

PROBLEM: Sentence: 'a man teaching a little boy to brush his teeth'. Find frequency of the letter 't'

SOLUTION:
6