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

Sentence: 'a bed with a dog laying on it next to two laptop computers'. Find frequency of the letter 'n'
3

Sentence: 'a girl playing with a frisbee while people watch'. Find frequency of the letter 'e'
5

Sentence: 'a big travel van parked in a loading lane of a hotel'. Find frequency of the letter 'l'
4