Correct answer: (2, 38)
The minimum value of x + y occurs when x is at its lowest (-7) and y at its lowest (9), resulting in -7 + 9 = 2. The maximum occurs when x is at its highest (18) and y at its highest (20), giving 18 + 20 = 38. Since x and y do not include their endpoints, the sum x + y will also not include 2 and 38, leading to the interval (2, 38).