D2.6. Three infinite uniform sheets of charge are located in free space as follows: 3 nC/m² at z = -4, 6 nC/m² at z = 1, and -8 nC/m² at z = 4. Find E at the point: (a) PA(2, 5, -5); (b) PB(4, 2, -3); (c) Pc(-1, -5, 2); (d) PD(-2, 4, 5).