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

Sentence: 'a small white dog looking out a car window'. Find frequency of the letter 'l'
3

Sentence: 'a grapefruit, toast, coffee and other items are on a tray'. Find frequency of the letter 't'
6

Sentence: 'a man that is laying down on a surfboard in the water'. Find frequency of the letter 's'
2