There is no image? Please input an image so I can try to help :)
The first figure has 3 angles, the second one has 4 angles, the third one has 5 angles so the next one will have 6 angles.
The violet figures inside stick with each side of the outer figures in the middle, so the last figure will look more less like in the attachment.
We have the following:

solving for x

The solution of x is equal to 28, therefore 12 is not a solution of the equation