If the soda can is a cylinder, which is most likely, than that means we need to find the height of the cone. The formula for volume of a cylinder is V= пr^2h (look at the pic for clearer formula) and we know the diameter of the soda can is 6, we know the radius is 3 because diameter is a line reaching from one point of the circle to the other. Radius is a line reaching from the center of the circle to the outside as shown in the image. We divide pi (you can put in the calculator 3.14) from 21, then we get 6.688 (if we round up) and then you must look at the formula now

it looks like
6.688=r^2h

that means we must find 3^2
that basically means 3x3 which is 9

then you have to divide that from 6.688

then you get 0.743

that is your height.

now we must find the volume of the cone. The formula for that is

V=пr^2(h/3)

now lets plug in our info

V=(3.14)(9)(0.743/3)

you get 6.999