A closed cuboid water tank is made of steel sheet that is 2.5 cm thick. The outer dimensions of the tank are
2.15 m × 1.5 m × 1.1 m. Find the capacity of the tank, and the volume of steel used to construct it. Also find the total surface area of the tank.

External dimensions of the cube are
l = 215 cm, b = 150 cm, h = 110 cm
Since the sheet is 2.5 cm thick, the internal dimensions are
l = (215 - 5) cm = 210 cm, b =(150 - 5) cm = 145 cm,
h = (110 - 5) cm = 105 cm
 
∴ External volume = (215 × 150 × 110) cm³
                            = 3547500 cm³
Internal volume  = (210 × 145 × 105) cm³
                        = 3197250 cm³
Capacity of tank = internal volume 
                       = 3197250 cm³
                       = 3.19725 m³
Volume of steel used = External volume - Internal volume
                           = (3547500 - 3197250) cm³
                           = 350350 cm³
                           = 0.35025 m³
Total surface area = 2(lb + bh + lh)
= 2 × (2.15 × 1.5 + 1.5 × 1.1 + 2.15 × 1.1) m³
= 2 × (3.225 + 1.65 + 2.365) m³                              
= 14.48 m³