TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a double decker bus with a lot of people on board'. Find frequency of the letter 'l'

SOLUTION: 3

PROBLEM: Sentence: 'a guy surfs a wave with his surfboard'. Find frequency of the letter 's'

SOLUTION: 4

PROBLEM: Sentence: 'large series of signs on a city street post'. Find frequency of the letter 'g'

SOLUTION:
2