the choices are 10 12 6 8
Find the area of the rectangle first.
Area = 4 x 16 = 64 square units
Then take the square-root of this value to find the side length of square.
length of square = √64 = 8 units
Or you can set up an equation to reduce the number of steps.
Area of rectangle = Area of square
(4 x 16) = x^{2}
where x is the length of square. From here, solve for x.
64 = x^{2}
8 = x