The quotient of a number and 2, increased buy 9 is -15

Haley buys 9 pounds of apples for $3. how many pounds of apples can she buy for $1?

The total cost of anja’s trip to the dentist was $628.35. she paid a flat fee of $89.95 which included the checkup and cleaning and then had 4 cavities filled, each of which cost the same amount. which shows the correct equation and value of x, the cost of each cavity filling?

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