TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a crowd of people standing in front of a green train'. Find frequency of the letter 'g'

SOLUTION: 2

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

SOLUTION: 4

PROBLEM: Sentence: 'a man riding on the back of a white horse next to other horses'. Find frequency of the letter 'o'

SOLUTION:
6