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

Sentence: 'a man using a video game controller in a room'. Find frequency of the letter 'n'
4

Sentence: 'a person is performing a stunt on a snowboard'. Find frequency of the letter 'p'
2

Sentence: 'a tennis player getting ready for his serve'. Find frequency of the letter 'y'

2