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

Sentence: 'a guy surfs a wave with his surfboard'. Find frequency of the letter 's'
4

Sentence: 'an area that has surrounded by a metal fence'. Find frequency of the letter 'o'
1

Sentence: 'a very attractive family room with a view of the river'. Find frequency of the letter 'v'

4