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

Example Input: Sentence: 'two pepperoni pizzas and a cup on a counter'. Find frequency of the letter 'u'
Example Output: 2

Example Input: Sentence: 'pizza with different vegetables sitting on top of a wooden slab'. Find frequency of the letter 'o'
Example Output: 5

Example Input: Sentence: 'a juicer attached to the top of a bike'. Find frequency of the letter 'h'
Example Output:
2