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

Sentence: 'a person dressed all in black snowboarding down a slope'. Find frequency of the letter 'e'
4

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

Sentence: 'a plane that is flying in the sky'. Find frequency of the letter 'i'
3