13. (12 points) In a cage, there are chickens and rabbits, with a total of 28 heads. The total number of rabbit feet is 12 more than 3 times the total number of chicken feet. How many rabbits are there in the cage?
【Answer】Solution:
Assume all are rabbits, then there are a total of $28 \times 4=112$ (feet)
Chickens have $(112-12) \div(3 \times 2+4)=10$ (chickens)
Rabbits $28-10=18$ (rabbits)
Answer: There are 18 rabbits in the cage.