This question is essentially asking you to find the surface area of the box.
The formula for SA on a rectangular prism is: 2(L*W+L*H+W*H)
L=Length W=Width H=Height
Lets input the information we know:
2(20*8+20*30+8*30)
Follow BEDMAS
2(160+600+240)
2(760+240)
2(1000)
2*1000
=2000
The box will need 2000 centimeters squared of material.
Hope this helps!
-Benjamin