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

Sentence: 'two people under an umbrella while walking down a sidewalk'. Find frequency of the letter 'i'
3

Sentence: 'a glass vase sits between two statues'. Find frequency of the letter 'o'
1

Sentence: 'five people stand in a room with many laptops on the desks'. Find frequency of the letter 'r'

1