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

Example Input: Sentence: 'one woman holding a video game controller and standing next to another woman'. Find frequency of the letter 't'
Example Output: 5

Example Input: Sentence: 'a baseball player dropping his bat and starting to run'. Find frequency of the letter 'o'
Example Output: 2

Example Input: Sentence: 'a parking lot ticket machine stands at the entrance of a parking area'. Find frequency of the letter 'h'
Example Output:
2