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

Example Input: Sentence: 'a man pushing a cart full of bananas'. Find frequency of the letter 'u'
Example Output: 2

Example Input: Sentence: 'a dog on a couch near many pillows'. Find frequency of the letter 'p'
Example Output: 1

Example Input: Sentence: 'apples pear and orange in white fruit bowl'. Find frequency of the letter 'p'
Example Output:
3