Whats the opposite intger of 6.72

Beth makes batches of bluberry muffins and banna muffins. each batchis 6 muffins. she makes 2.5 batches of bluberry muffins. how many batches of bananna muffins should beth make if she wants to have a total of 60 muffins?

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

Anyone know these questions? i need ,.