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

Example Input: Sentence: 'a woman holds the reins of a saddled horse'. Find frequency of the letter 'm'
Example Output: 1

Example Input: Sentence: 'man in a radio studio wearing a suit in front of a microphone'. Find frequency of the letter 't'
Example Output: 3

Example Input: Sentence: 'a beautiful baby laying next to a teddy bear'. Find frequency of the letter 'd'
Example Output:
2