TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a toasted sub sandwich is next to a salad'. Find frequency of the letter 'a'

SOLUTION: 6

PROBLEM: Sentence: 'a display case filled with lots of different clocks'. Find frequency of the letter 'w'

SOLUTION: 1

PROBLEM: Sentence: 'two people sitting on a stone surface with their faces covered by a blue umbrella'. Find frequency of the letter 's'

SOLUTION:
4