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

Example Input: Sentence: 'a young girl is brushing her teeth in this dated photo'. Find frequency of the letter 't'
Example Output: 5

Example Input: Sentence: 'a couple is cutting in to a cake at a wedding'. Find frequency of the letter 'd'
Example Output: 2

Example Input: Sentence: 'a man and a woman are playing on the wii'. Find frequency of the letter 'p'
Example Output:
1