Naomi is building a circuit board. the final microchip should have a surface area of 864 square millimeters. the height of the microchip can be a maximum of 4 millimeters. What are the maximum dimensions of the microchip she can use? The height of the microchip is 2x and the width is x.
A. 6 mm and 12 mm
B. 9 mm and 18 mm
C. 12 mm and 24 mm
D. 8 mm and 16 mm