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

Example Input: Sentence: 'two giraffes, one standing and one laying down'. Find frequency of the letter 'g'
Example Output: 3

Example Input: Sentence: 'a pizza pie sitting on a wooden table with tongs'. Find frequency of the letter 't'
Example Output: 5

Example Input: Sentence: 'some people are eating desserts with fresh fruit on them'. Find frequency of the letter 'd'
Example Output:
1