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

Example Input: Sentence: 'a bed with a dog laying on it next to two laptop computers'. Find frequency of the letter 'n'
Example Output: 3

Example Input: Sentence: 'a very big nice looking living room with nice furnishings'. Find frequency of the letter 'e'
Example Output: 3

Example Input: Sentence: 'a little boy sitting on a bed in a bedroom'. Find frequency of the letter 'e'
Example Output:
3

