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

Example Input: Sentence: 'people seated on a table looking very happy'. Find frequency of the letter 'g'
Example Output: 1

Example Input: Sentence: 'a group of giraffes walk together by a hill'. Find frequency of the letter 'b'
Example Output: 1

Example Input: Sentence: 'there is a very old rusted truck that is parked outside'. Find frequency of the letter 'e'
Example Output:
6