Question 3479
With o problem like this, it is good to draw some sketches. 
Draw the unfolding (a square with in each corner a smaller square with a side of 3cm) The volume of the box (with a square basesurface) is base² x height and that has to be 48 cm³. When you draw the unfolding, you can see that the height is 3 cm (cause of the smaller squares you cut). b² x h = 48 so
b²=48/3=16 thus b=4cm. Now we can calculate the surface of the tin:
A=(b+2*3cm)² This gives a surface of 100cm².

I hope you understand it, I tried to put a picture on this but it didn't work. You can always mail me at gurdebeke_pieter@hotmail.com