You have a cube of gold. Your friend (even though she may not be your friend much longer) has a cube of gold that is twice as long (and wide and high). Your friend's cube weighs as much as yours, and it has times the surface area.
You also have a spherical diamond. Your friend has a spherical diamond of twice the diameter of yours. Your friend's diamond weighs as much as yours, and it has the surface area.
Hint: Understand scaling.