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

[Q]: Sentence: 'two computers and a laptop set up on a desk'. Find frequency of the letter 'r'
[A]: 1


[Q]: Sentence: 'flower in a vase full of water sitting on a stand '. Find frequency of the letter 'l'
[A]: 3


[Q]: Sentence: 'this is a picture of a aircraft in the air'. Find frequency of the letter 'u'
[A]:
1