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

Sentence: 'a laptop computer with pictures of giraffes on the homescreen'. Find frequency of the letter 'o'
5

Sentence: 'two metal  benches on an empty train platform'. Find frequency of the letter 'n'
4

Sentence: 'hamburger with lettuce and tomato, served with french fries covered in ketchup'. Find frequency of the letter 'e'

10