we can write the volume of a can (I assume cylindrical) in terms of its height and radius:
pi*r^2*h = V
If our volume is fixed at 1000 cm^3, then for given r, our h is determined.
The surface area of the same cylinder is given by:
A =2*Pi*r*h + 2*pi*r^2
The first term is the area of the cylindrical part of the can, the second term corresponds to the top and bottom disks of the can.
A is the quantity we wish to minimize. From our first equation,
h = V/(pi*r^2), so substitute this into the equation for A:
A(r) = 2*Pi*r*V/(pi*r^2) + 2*pi*r^2
= 2*1000/r + 2*pi*r^2
Now I assume you can use calculus to find the minimum of the function A with respect to the variable r, so finish the job.