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

Example Input: Sentence: 'a doll with huge eyes and black hair with blunt bangs holds a red umbrella'. Find frequency of the letter 'e'
Example Output: 5

Example Input: Sentence: 'a full plate of food that includes rice and broccoli and carrots'. Find frequency of the letter 's'
Example Output: 2

Example Input: Sentence: 'a group of friends sitting on a bench near the water'. Find frequency of the letter 'g'
Example Output:
2