If the length of the radius in a circle is increased (or in this case, doubled) the circumference changes along with it. Because, remember; radius is half of circumference, so if the radius changes it only makes sense for the or circumference to change as well. To find the area of the circle you need the circumference, and if the radius has been changed, so will the circumference, and if the circumference has changed, so will the area. Get it? Hope I helped