A Lawnmower Using a 40 M Extension Cord Cuts Grass $\pi$

Multiple Choice

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.

A) 160 $\pi$ m²
B) 80 $\pi$ m²
C) 120 $\pi$ m²
D) 320 $\pi$ m²
E) 225 $\pi$ m²