C. The playable area has a width of 9 inches and a height of 6 inches.
There are a number of ways you can get there.
1. Check the answers to see which have the right area and aspect ratio.
2. If the screen were 3:2 (inches), its area would be 6 in². The area of 54 in² is 9 times that value, so the actual screen dimensions are √9 = 3 times 3:2. That is, they are width:height = 9:6 inches — matches selection C.
3. You can write equations for width and height and solve.
Substituting w=3/2·h into the second equation gives
... (3/2)h·h = 54
... h² = 36 . . . . . multiply by 2/3
... h = √36 = 6 . . . . square root, result in inches . . . . matches selection C