TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a guy surfs a wave with his surfboard'. Find frequency of the letter 's'

SOLUTION: 4

PROBLEM: Sentence: 'a man is water skiing on a river'. Find frequency of the letter 'r'

SOLUTION: 3

PROBLEM: Sentence: 'a zebra standing alone on a patch of grass and dirt'. Find frequency of the letter 'g'

SOLUTION:
2