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

Example Input: Sentence: 'a glass a rope and a pair of scissors'. Find frequency of the letter 's'
Example Output: 6

Example Input: Sentence: 'a bedroom with a neatly made bed and a laptop'. Find frequency of the letter 'l'
Example Output: 2

Example Input: Sentence: 'assorted types of pizza and bottles on a table'. Find frequency of the letter 'n'
Example Output:
2