Problems Solving.?

Question

1. A closed box, whose length is twice its width, is to have a surface of 192 square inches. Find the dimensions of the box when the volume is maximum.

2. What number exceeds itself by the maximum amount?

Answer 1

x= width,y= height
S=2*x^2*2+2xy+4xy = 4x^2 +6xy=192
V=2x^2y maximum

y= (192-4x^2)/6x = (96-2x^2)/3x
V=1/3 (192x-4x^3)
V´=1/3(192-12x^2)=0 so x= sqrt(16)= 4 y=16/3 and length=8 inches
I don´t understand 2nd question