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

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

[Q]: Sentence: 'a full plate of food that includes rice and broccoli and carrots'. Find frequency of the letter 's'
[A]: 2

[Q]: Sentence: 'a little girl sitting in front of a white bag filled with green apples'. Find frequency of the letter 'r'
[A]:
3