There’s no way to know for sure without knowing the shape of the blanket. An area of 12 could be 4 by 3, for instance. Then the perimeter (which tells you the length of fabric you need for the border) would be 14. But it could also be 6 by 2 (perimeter 16) or round (perimeter about 12.27) or lots of other things.
You got it.
Blanket 3x4 needs 14 untis of border.
Blanket 2x6 needs 16 units of border.
Blanket 1x12 needs 26 units of border.
There is not enough information to know which it is.
Good point!
That’s right, you cannot know unless you know the shape.
The minimum length would be if it were square — each side would be the square root of 12, or 2 X square root of 3.
So if each side was 2X sqrt 3, total would be 8X sqrt 3.
Sqrt of 3 is 1.732 -, so you’d need not less than 13.86 inches. Any other dimensions and its longer.