Answer:
2 mm
Step-by-step explanation:
Let x be the sides of the original square,
then the area of the original square is x^2
The sides of the new square is x + 6
The area is (x + 6)^2
Then (x + 6)^2 = 16*x^2
Take square root on both sides and get
x + 6 = 4x,
3x = 6
so x = 2 mm
