The radius of the cone bottom is:12.56/(2 * 3.14) = 2m.

The volume of sand pile is: 3.14 * 2 * 2 *1.2/3 = 5.024 cubic meters.

Therefore, the paving thickness of rectangular silo is: 5.024/(4 * 3) = 0.42 m.

two

It is known that 1 cm3 steel weighs 7.8 grams.

The radius of the bottom circle is 30/5=6 cm.

The radius of the small circle is 6- 1 = 5cm.

The volume of the tube is equal to the volume of the big cylinder.

The volume of the tube is: 3.14 * 6 * 6 * 30-3.14 * 5 * 30 =1036.2 cubic centimeters.

So the weight of the tube is1036.2 * 7.8 = 8082.36g.