The picture shows the frame with the picture inside. You should be able to use the picture to show you all you need to know. All lengths are in inches and to scale.
However, the frame border is not the same all round, being 6 inches for the 12-inch side of the picture, and 9 inches for the 18-inch side. So a lot depends on what is meant by twice the size of the picture, that is, twice the length and twice the width. But it could also mean twice the area=2×12×18=432 sq ins.
In this case the answer is different. If x is the frame border width all round then we can write:
(2x+12)(2x+18)=432, 4x²+60x+216-432=0, 4x²+60x-216=0, x²+15x-54=0=(x-3)(x+18).
Therefore x=3 inches all round and the frame is 12+6=18 inches by 18+6=24 inches, as shown below:
