TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'two persons standing outside a moving sub train'. Find frequency of the letter 'a'

SOLUTION: 3

PROBLEM: Sentence: 'soccer players on opposite teams fight for control over a ball'. Find frequency of the letter 't'

SOLUTION: 4

PROBLEM: Sentence: 'a person's hand on a suitcase that is open'. Find frequency of the letter 'h'

SOLUTION:
2