Which bird is closest and by how much

What is the slope simplify your answer and write it as a proper fraction, improper fraction, or integer

Amuffin recipe, which yields 12 muffins, calls for cup of milk for every 1 cups of flour. the same recipe calls for cup of coconut for every cup of chopped apple. to yield a batch of 30 muffins, how much flour will be needed in the mix?

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?