A ring placed along y 2 + z 2 = 4, x = 0 carries a uniform charge of 5 μ C/m. ( a ) Find D at P(3,0,0). ( b ) If two identical point charges Q are placed at (0, - 3,0) and (0,3,0) in addition to the ring, find the value of Q such that D = 0 at P