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

Example Input: Sentence: 'red chair next to side table with lamp in residential home'. Find frequency of the letter 'm'
Example Output: 2

Example Input: Sentence: 'a gray colored pigeon that is perched on a railing outside of a building, with other buildings in the background'. Find frequency of the letter 'e'
Example Output: 7

Example Input: Sentence: 'two white electric toothbrushes are in their stands'. Find frequency of the letter 't'
Example Output:
7