geometry
posted by Piggy .
The surface area of a right rectangular prism is 112 sq units. The height is twice the width. The length is 4 units more than the height . Find the volume.

width  x
length  x+4
height  2x
surface area
= 2(x)(x+4) + 2(x)(2x) + 2(2x)(x+4)
= 112
2x^2 + 8x + 4x^2 + 4x^2 + 16x = 112
10x^2 + 24x  112=0
5x^2 + 12x  56 = 0
x = (12 ± √1264)/10
= 2.355 or a negative
width = 2.355
length = 6.355
height = 4.711
check:
2(2.355(6.355) + 2(2.355)(4.711) + 2(6.355)(4.711) = 112 
volume = (2.355)(6.355)(4.711) = .....