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: 'a view from a bathroom shows an open door'. Find frequency of the letter 'o'

SOLUTION: 7

PROBLEM: Sentence: 'a large airplane flying high up in the air'. Find frequency of the letter 'i'

SOLUTION:
5