Question 369984
let width be x
length = x+5
height = x-3
..
Area of 4 walls = 2*LH + 2*WH
= 2*(x-3)(x+5)+2*x*(x-3)
=2(x^2+2x-15)+2x^2-6x
=2x^2+4x-30+2x^2-6x
=4x^2-2x-30
...
Area of ceiling & floor 
Area = 2 * LW 
Area = 2*x*(x+5)
Area = 2x^2+10x
..
4x^2-2x-30 =2x^2+10x+240
2x^2-12x-270=0
/2
x^2-6x-135=0
x^2-15x+9x-135=0
x(x-15)+9(x-15)=0
(x-15)(x+9)=0
x= 15  feet the width
length = x+5 = 15 +5 = 20 feet
height = x-3 = 15-3 = 12 feet
...
m.ananth@hotmail.ca