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 desk covered in notepads, a laptop and other devices'. Find frequency of the letter 'c'
2

Sentence: 'a large homemade pizza with spinach and chicken atop it'. Find frequency of the letter 'n'

3