In this task, you need to count the number of times the given letter appears in the given sentence.

Sentence: 'young girl playing with refrigerator magnet while kneeling on floor'. Find frequency of the letter 'n'
6

Sentence: 'a crowd of people standing in front of a green train'. Find frequency of the letter 'g'
2

Sentence: 'a living room filled with furniture and surrounded by windows'. Find frequency of the letter 'r'
5