Answer:
11,664 in³
Step-by-step explanation:
For a square side length of x, the girth is 4x and the length of the parcel is then allowed to be up to 108-4x.
The total volume is the product of the edge lengths, so is ...
V = (108 -4x)(x²) = -4x³ +108x²
This will be a maximum where its derivative is zero:
dV/dx = -12x² +216x = 0 = -12x(x -18)
This is zero for x=0 and for x=18.
The maximum volume parcel is 18 in by 18 in by 36 in, and has a volume of ...
(18 in)(18 in)(36 in) = 11,664 in³
