These are the MCQS related to Physics and I need the Solution of these

witwisesA conducting spherical shell with inner radiusa - 2 cm and outer radius b - 2a has a positivepoint charge Q = 0.2nC located at its center.10The total charge on the shell is -3Q, and it isinsulated from its surroundings.What is the surface charge density on the outersurface of the conducting shell?(Take 7 = 3 and 1/(4760) = 9 x 10" N. m?/C2)-20.8 nC/m2-13.89 nC/m-125 nC/m2-82.3nC/m?-23.15 nC/m2