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 tennis player that is running to get the tennis ball'. Find frequency of the letter 't'

SOLUTION: 7

PROBLEM: Sentence: 'a person is cutting blue plastic with a pair of scissors'. Find frequency of the letter 's'

SOLUTION:
7