The length of the sides in the reflected figure will still be 6 units. Reflection across the x axis does not change the size or shape of the square, it simply changes its orientation.
When a square is reflected across the x-axis, the y-coordinates of the vertices are negated. Since all sides of a square are equal in length, the length of the sides in the reflected figure remains the same. Therefore, the sides of the reflected figure will also be 6 units in length.
