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

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

Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'
2

Sentence: 'a bed with white sheets that has been laid in'. Find frequency of the letter 'e'
6