Since area = length * width the area of this is 6 * 2 = 12 units^2. The perimeter is 2*length + 2*width = 12 + 4 = 16 units.
If you reduce the length by 1 and increase the width by 1, the perimeter stays the same:
2*5 + 2*3 = 10 + 6 = 16 units. However, the area changes:
5 * 3 = 15 units^2
Hope this helps!