Wallpaper, 312 m long and 25 cm wide is required to cover the walls of a room. Length of the room is 7m and its breadth is twice its height. Determine the height of the room.

 Height of room—x:
2(x[2x]) + 2(7x) = 312(25/100)
4x² + 14x = 78
x² + 1.75x = 19.5 + 1.75²
x² + 1.75x = 19.5 + 3.0625
(x + 1.75)² = 22.5625
x + 1.75 = 4.75
x = 3

Answer: 3 meters is the height of the room.

Proof:
2(3[2{3}]) + 2(7[3]) = 312(25/100)
36 + 42 = 78
78 = 78

Proof:
2(7[5.0243613]) + 2(5.0243613[5.0