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 view from a bathroom shows an open door'. Find frequency of the letter 'o'
Example Output: 7

Example Input: Sentence: 'a young man kicking a soccer ball around on a field'. Find frequency of the letter 'e'
Example Output:
2