A 5 g piece of Styrofoam carries a net charge of −0.5 µC and floats above the center of a very large horizontal sheet of plastic that has a uniform charge density on its surface. What is the charge per unit area on the plastic sheet? The acceleration due to gravity is 9.8 m/s 2 and the permittivity of free space is 8.85419 × 10−12 C 2 /N/m2 . Answer in units of µC/m2 .