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

Sentence: 'a crowd of people skiing and enjoying the snow'. Find frequency of the letter 'o'
5

Sentence: 'a group of people having dinner and drinking wine'. Find frequency of the letter 'r'
3

Sentence: 'commuter train at platform in populated city on sunny day'. Find frequency of the letter 'p'

3