TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'an commercial airline airplane flies above the clouds'. Find frequency of the letter 'n'

SOLUTION: 3

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

SOLUTION: 1

PROBLEM: Sentence: 'a smiling man with glasses on, wearing a cook's hat'. Find frequency of the letter 'a'

SOLUTION:
6