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

Sentence: 'a woman is taking a sip of a drink from a glass'. Find frequency of the letter 'i'
4

Sentence: 'the counter of a doctor's office, including a laptop, cotton swabs, and tongue depressors'. Find frequency of the letter 'g'
2

Sentence: 'a group of people posing on motorcycles for a photo'. Find frequency of the letter 'n'
2