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

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

[Q]: Sentence: 'two elephants facing each other touching trunks in an enclosure'. Find frequency of the letter 'f'
[A]: 1

[Q]: Sentence: 'the train is going down the railroad tracks'. Find frequency of the letter 'g'
[A]:
2