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

Sentence: 'a girl that has a kite in the air'. Find frequency of the letter 'r'
2

Sentence: 'the child is waving a small flag as she stands near two women'. Find frequency of the letter 'g'
2

Sentence: 'hamburger with lettuce and tomato, served with french fries covered in ketchup'. Find frequency of the letter 'e'
10