Minimising the surface area of a cylindrical box

A company manufactures cylindrical boxes (with a base and lid) of fixed volume V₀ = 500 cm³. The total surface area of metal used is given by S(r) = 2πr² + 1000/r, where r is the radius in cm (r > 0). Determine, giving a detailed explanation of your reasoning (calculation of S'(r) and analysis of its sign), the value of r that minimises the surface area, then give an approximate value for this minimum surface area.