Look at the table for each type of bird. 5x=15. 6x=18. 10x=30. What would you multiply each of those by to get your answer and find the difference? 5x=15; x= 3. It is the same for each number. So the difference is by 3. I think if I understand this correctly, that would be how you do it. Does this help?
13 ft is the right answer
1. S= 5/6 or 0.833333
2. 0