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

Example Input: Sentence: 'one woman is arranging the other woman's hair'. Find frequency of the letter 'o'
Example Output: 4

Example Input: Sentence: 'a stuffed animal sitting on an empty bed'. Find frequency of the letter 'u'
Example Output: 1

Example Input: Sentence: 'a young girl sitting under a flying kite'. Find frequency of the letter 'u'
Example Output:
2