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

Sentence: 'a man riding a white surfboard on a large wave'. Find frequency of the letter 'a'
7

Sentence: 'hotel towels with sunglasses perched and hotel business cards and catalog'. Find frequency of the letter 'o'
4

Sentence: 'two pizzas on a table being served at a restaurant'. Find frequency of the letter 'r'
3