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: 'a young man riding a skateboard near a forest'. Find frequency of the letter 'd'
2

Sentence: 'a large blue octopus kite flies above the people having fun at the beach'. Find frequency of the letter 'p'
3