TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'some sheep are standing in a grassy field'. Find frequency of the letter 'n'

SOLUTION: 3

PROBLEM: Sentence: 'a herd of zebra standing on top  of a grass covered field'. Find frequency of the letter 'e'

SOLUTION: 5

PROBLEM: Sentence: 'a croissant sandwich sitting on a green plate'. Find frequency of the letter 'e'

SOLUTION:
3