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

[Q]: Sentence: 'a cat that is standing next to an open suitcase'. Find frequency of the letter 'e'
[A]: 3

[Q]: Sentence: 'a man walking a large elephant down a dirt road'. Find frequency of the letter 'g'
[A]: 2

[Q]: Sentence: 'two laptop computers sitting on top of a white table'. Find frequency of the letter 'f'
[A]:
1