A very large plane of charge is oriented horizontally and has a constant charge distribution over the plane. A small insulating ball has charge +8.78 nC and mass 0.076 g. If the levitates 2.62 cm beneath the plane, and remains stationary, what is the magnitude of the surface charge density on the charged plane? Write your answer to three significant figures in nC/cm2 (nanoCoulombs per square centimeter).