A 200-g piece of styrofoam carries a net charge of -0648

Question

Problem: A 20.0-g piece of Styrofoam carries a net charge of -0.648 µC and is suspended in equilibrium above the center of a large, horizontal sheet of plastic that has a uniform charge density on its surface.

Part A: What is the charge per unit area on the plastic sheet?

_______________µC/m²

Please include each step and the equations you used to determine the charge per unit area on the plastic sheet. Thanks!