A small sphere with mass 3.50 g hangs by a thread between two parallel vertical plates that are 6.00 cm apart. The sphere carries charge q=8.90x106 C. The plates are insulating, and left and right have uniform surface charge densities + and , respectively. The space between the plates is filled with air. Find the value of and the magnitude of the potential difference V which lead the thread to assume an angle of 30.0 degrees with respect to the vertical