The answer that you submitted suggests that you have used or calculated the known value of charge not the unknown value. If you cannot find a section below that helps resolve your error, please visit the feedback discussion page or try the charged spheres demo question again.
The value that you submitted is the known charge from the question statement. This error could be due to a misunderstanding of the electric field for a charged sphere.
Please try again.
The value that you submitted is the known charge with an incorrect sign from the question statement. Submission of the known charge can indicate a conceptual difficulty with Coulomb's law and/or the electric field.