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

[Q]: Sentence: 'a group of people having dinner and drinking wine'. Find frequency of the letter 'r'
[A]: 3

[Q]: Sentence: 'a silver train crossing the road on tracks'. Find frequency of the letter 'r'
[A]: 5

[Q]: Sentence: 'a bunch of ducks on a field with feather all around'. Find frequency of the letter 'b'
[A]:
1