Answer:
A prism is a solid object having two identical bases, hence the same cross section along the length. Prism are called after the name of their base. A rectangular prism is a solid whose base is a rectangle. Multiplying the three dimensions of a rectangular prism: length, width and height, gives us the volume of a prism:

FOR THE ORIGINAL PRISM WE HAVE THE FOLLOWING DIMENSIONS:

In fact, the volume is
because:

Now the height of the prism was changed from 3 centimeters to 6 centimeters to create a new rectangular prism, therefore:
FOR THE NEW PRISM WE HAVE THE FOLLOWING DIMENSIONS:

So the new volume is:

What do we know about the volume of the new prism?
Well, the volume has increased from
and since
we can say that the new volume is two times the original volume.