Near the surface of Earth, an electric field points radially downward and has a magnitude of approximately 100 N/C.
1)What charge (magnitude and sign) would have to be placed on a penny that has a mass of 2.50 g to cause it to rise into the air with an upward acceleration of 1.990 m/s2? (Express your answer to three significant figures.)
How can one approach this question? I got 2.94×10^-4 but it keeps saying it is incorrect.