Let the length, breadth & height of the rectangular box be 3x cm, 2x cm & x cm respectively.
According to the problem,
3x . 2x . x = 384
or, 6x3 = 384
x3=\frac{384}{6}= 64 = (4)3
\therefore x = 4
Length = 3 × 4 = 12 cm.
Breadth = 2 × 4 = 8 cm.
& Height = 1 × 4 = 4 cm.
The total area of 6 surfaces of the rectangular parallelopiped
= 2(l × b + l × h + b × h)
= 2(12 × 8 + 12 × 4 + 8 × 4) sqcm.
= 2(96 + 48 + 32) sqcm.
= 2(96 + 48 + 32) sqcm = 2 × 176 sq cm = 352 sq cm