In this task, you need to count the occurrences of the given word in the given sentence.

Example Input: Sentence: 'a delivery truck for a library parked by a meter'. Count the occurrences of the word 'a' in the given sentence.
Example Output: 3

Example Input: Sentence: 'she was walking down the side walk with her umbrella open'. Count the occurrences of the word 'down' in the given sentence.
Example Output: 1

Example Input: Sentence: 'a young man riding a wave on a white surfboard'. Count the occurrences of the word 'a' in the given sentence.
Example Output:
3