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

Input: Consider Input: Sentence: 'a grey hummingbird by fence and tree branches'. Find frequency of the letter 'y'

Output: 2

Input: Consider Input: Sentence: 'a train going over a bridge with some buildings in the background'. Find frequency of the letter 'd'

Output: 3

Input: Consider Input: Sentence: 'the kitchen has a built-in oven and microwave next to a tall built-in wine rack'. Find frequency of the letter 'e'
Output: 6