Can you give me some step-by-step instructions for this math problem: A zoo has 8 parrots. It 3 times the number of snakes than parrots and 2 times the number of monkeys than snakes. The number of elephants is half the number of parrots and snakes added up, and there are 3 fewer zebras than elephants. What is the difference in number between the zebras and the monkeys?