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

Input: Consider Input: Sentence: 'two people are riding on canoes down a river'. Find frequency of the letter 'e'

Output: 5

Input: Consider Input: Sentence: 'a metallic stove top oven inside of a wooden kitchen'. Find frequency of the letter 'v'

Output: 2

Input: Consider Input: Sentence: 'a small microwave in a public eating area'. Find frequency of the letter 'r'
Output: 2