Atiny ball (mass = 0.010 kg) carries a charge of -24c. what is the electric field magnitude that would cause the ball to float above the ground?

Use the relation between electric force and electric field and the concept of gravitational force to calculcate the electric field.  The electric force is given by

And the gravitational force is

For the ball to float above the ground, the magnitude of electric force on the ball must be equal to the magnitude of the gravitational force. That is must be a equilibrium condition, so,

Replacing the values we have that,

Therefore the electric field magnitude that would cause the ball to float above the ground is

neither accurate nor precise.