Hi,
    I was going through a couple of questions when I came upon these 2 questions which I can't get the answer to. So, if anyone can help me with them then that would be great:D. The questions are:
(1) A point charge  with q1 = +0.50 µC is placed 0.50m to the left of a second point charge with q2 = 4q1. What are the magnitudes and directions of the forces on the two charges?
(2) Three identical point charges q are placed at each of the three corners of a square of side L. Find (a) the magnitude and direction of the electric field at the centre of a square and (b) the net electric force on a point charge -3q placed at the centre of the square.
Thanks,
Peter.