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

Sentence: 'a group of people stand inside of a big room'. Find frequency of the letter 'o'
6

Sentence: 'a downhill skier with snow plumes behind them'. Find frequency of the letter 'i'
4

Sentence: 'a giraffe sticking its head into a truck on dirt field'. Find frequency of the letter 'r'

3