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

Example Input: Sentence: 'a lady mixes some things in a blender as people look on'. Find frequency of the letter 'i'
Example Output: 3

Example Input: Sentence: 'the miniature, elaborate exhibit depicts an ancient boating scene'. Find frequency of the letter 'n'
Example Output: 6

Example Input: Sentence: 'woman intently plays wii in her living room'. Find frequency of the letter 'w'
Example Output:
2