TASK DEFINITION: In this task, you need to count the number of times the given letter appears in the given sentence.
PROBLEM: Sentence: 'a group of cows that are standing in the grass'. Find frequency of the letter 'g'

SOLUTION: 3

PROBLEM: Sentence: 'a man and several white red and blue airplanes'. Find frequency of the letter 'u'

SOLUTION: 1

PROBLEM: Sentence: 'a dog hangs out the driver side of a moving car'. Find frequency of the letter 'd'

SOLUTION:
3