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

Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'
2

Sentence: 'a glass a rope and a pair of scissors'. Find frequency of the letter 's'
6

Sentence: 'a person and surf board handling a wave'. Find frequency of the letter 'a'

6