Clare noticed mold on the last slice of bread in a plastic bag. The area covered by the mold was about 1 square
millimeter. She left the bread alone to see how the mold
would grow. The next day, the area covered by the mold
had doubled, and it doubled again the day after that.

If the doubling pattern continues, how many square
millimeters will the mold cover 4 days after she
noticed the mold? Show your reasoning.