A lawnmower using a 40 m extension cord cuts grass in a circular area. It is discovered that there is a knot in the cord, and untying it lengthens the cord to 42 m. Using an appropriate linearization, estimate how much more area can be cut with the unknotted cord.
◦ 160π m2
◦ 80π m2
◦ 320π m2
◦ 120π m2
◦ 225π m2