You need to first figure out the dimensions of the rectangle.

A rectangle will only fold around the sides of the can, but not the base or the top of the can.

What information do you know?

You already know how tall the can is, namely, 12 cm. That means that the rectangle will be 12x12 cm... To be 144 cm2. Try it... Peel off the label of a plastic coca-cola bottle and notice how you get a nice rectangular label.

This means that the circumference of the can is 12 cm.

A rectangle will only fold around the sides of the can, but not the base or the top of the can.

What information do you know?

You already know how tall the can is, namely, 12 cm. That means that the rectangle will be 12x12 cm... To be 144 cm2. Try it... Peel off the label of a plastic coca-cola bottle and notice how you get a nice rectangular label.

This means that the circumference of the can is 12 cm.