A14.8-g piece of styrofoam carries a net charge of -0.742 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. what is the charge per unit area on the plastic sheet?

Base on your question where a 14.8g of piece of Styrofoam carries a net charge of -0.742C and is suspended in equilibrium above the center of a large, horizontal sheet of plastic so the ask of the problem is to calculate  the charge per unit area on the plastic sheet. The answer would be 21.96