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

Example Input: Sentence: 'supplies and tools are arranged on the floor with a hard hat and bag'. Find frequency of the letter 'n'
Example Output: 4

Example Input: Sentence: 'a picture of a toilet and toilet paper in a bathroom'. Find frequency of the letter 'o'
Example Output: 5

Example Input: Sentence: 'a small fruit is sitting on a cutting board next to scissors'. Find frequency of the letter 'o'
Example Output:
4