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

Example Input: Sentence: 'a laptop computer with pictures of giraffes on the homescreen'. Find frequency of the letter 'o'
Example Output: 5

Example Input: Sentence: 'a pizza is in a box on a table outside'. Find frequency of the letter 'u'
Example Output: 1

Example Input: Sentence: 'a woman that is standing in front of an oven'. Find frequency of the letter 'a'
Example Output:
5