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

Sentence: 'a person does a trick on a ramp on a snowboard'. Find frequency of the letter 's'
3

Sentence: 'man riding a skate board down the little board way'. Find frequency of the letter 'k'
1

Sentence: 'birds walking at waters edge in the rain'. Find frequency of the letter 'i'
4