Question 691485
Box is 20 cm wide x 30 cm long x 40 cm tall, so there are:
  2 x sides of size 20 x 30
  2 x sides of size 30 x 40
  2 x sides of size 20 x 40

So total surface area is
= (2 x 20 x 30) + (2 x 30 x 40) + (2 x 20 x 40)
= 1200 + 2400 + 1600
= 5200 sq cm