TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'this is a sign in front of a large cathedral'. Find frequency of the letter 'a'

SOLUTION: 5

PROBLEM: Sentence: 'a little boy that has a toothbrush in his mouth'. Find frequency of the letter 'r'

SOLUTION: 1

PROBLEM: Sentence: 'a greek-language signpost on a city street in the rain'. Find frequency of the letter 'r'

SOLUTION:
3