The surface area of a 4-meter-long cylindrical timber increased by 12.56 square decimeters after sawing it into two small columns The volume is () cubic decimeter

The surface area of a 4-meter-long cylindrical timber increased by 12.56 square decimeters after sawing it into two small columns The volume is () cubic decimeter

12.56/2=6.28dm2
4m=40dm
40*6.28=251.2dm2

There is a 12 meter long cylindrical timber. After sawing into 6 meters of timber, the surface area increases by 12.56 square decimeters. What is the volume of timber?
Use iron sheet to make a ventilation pipe with a diameter of 50 cm and a height of 3 m, and the joint of iron sheet is 5 cm. How many square meters of iron sheet is needed to make four such ventilation pipes?

1. Bottom area: 12.56 △ 2 = 6.28 square meters
6.28 × 12 = 75.36 M3
2. Bottom perimeter: 3.14 × 50 = 157 cm = 1.57 M
(1.57 × 3 + 0.05) × 4 = 19.04 square meters

There is a 1 meter long cylindrical steel, cut it into four sections, are cylindrical steel, surface area increased by 56.52 square decimeters, known per cubic decimeter of steel weight 7
There is a one meter long cylindrical steel, which is cut into four sections. The surface area is increased by 56.52 square decimeters. It is known that each cubic decimeter of steel weighs 7.8 kg. How many kg does this steel weigh?
"Calculate the formula and state the analysis of your method"

The surface area is increased by (4-1) * 2 = 6 times
56.52÷6=9.42…… This is the cross-sectional area
1 meter = 10 decimeters
42x10 = 94.2 cubic decimeter This is volume
7.8x94.2 = 734.76kg