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

[Q]: Sentence: 'a man riding on the back of a white horse next to other horses'. Find frequency of the letter 'o'
[A]: 6


[Q]: Sentence: 'the receipts from a meal at a restaurant are for  a sandwich, chili, and apple'. Find frequency of the letter 'u'
[A]: 1


[Q]: Sentence: 'a white airplane is in an upward flying position'. Find frequency of the letter 'l'
[A]:
2