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

Example Input: Sentence: 'city two way street with cars lined up on both sides'. Find frequency of the letter 'h'
Example Output: 2

Example Input: Sentence: 'a woman holds a wine glass upside down while wearing rabbit ears and staring at a bottle of wine'. Find frequency of the letter 'a'
Example Output: 11

Example Input: Sentence: 'one white cattle and one brown cattle are walking together'. Find frequency of the letter 'n'
Example Output:
5