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: 'a bowl of vegetables in a soup like substance next to a spoon'. Find frequency of the letter 'a'
Example Output: 5

Example Input: Sentence: 'a bike sitting next to a cup filled with coffee'. Find frequency of the letter 'e'
Example Output:
5