Answer:
18
Explanation:
So what you need to find is the scale factor which is the scale of the difference between two lengths.
So Figure A is smaller than Figure B, as can be easily detected with our eyes.
Figure A has a ratio of 1/2, as 6/12 is equal to 1/2.
Since B is the original, where A is a scaled version, it must also have the same ratio of 1/2, so twice 9 is 18, which is your answer.
You can also use fractions, by making Figure A into 1/2 because 1/2 = 6/12.
Figure B can turn into 9/x.
Since you know they are scaled factors, they have the same ratio since one is scaled larger or smaller than from the original.
Since it must follow the multiplication of 2 for the side length, 9 x 2 gives your answer.