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

Example Input: Sentence: 'soccer players on opposite teams fight for control over a ball'. Find frequency of the letter 't'
Example Output: 4

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

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