4.17 Three surface charge distributions are located in free space as follows: 10 μC/m² at x=2,-20 μC/m² at y = -3, and 30 μC/m² at z = 5. Determine E at (a) P (5, -1, 4), (b) R(0, -2, 1), (c) Q (3,-4, 10).