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

Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'
3

Sentence: 'a snowboarder making a jump of a snowy ledge'. Find frequency of the letter 'o'
4

Sentence: 'three woman are having a discussion in the kitchen'. Find frequency of the letter 'n'

5