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

Sentence: 'a man riding a skateboard up the side of a ramp'. Find frequency of the letter 'u'
1

Sentence: 'a man is water skiing on a river'. Find frequency of the letter 'r'
3

Sentence: 'a cut in half sub and other foods are ready to eat'. Find frequency of the letter 'o'

4