Solve the all parts of given problem:
Problem: Three equal positive point charges of magnitude Q = 12.00 uC are located at three corners of a square of edge length d = 4.9 cm. A negative charge -36.00 uC is placed on the fourth corner.
Part A: At the position of the negative charge, what is the magnitude of the electric field due to the three positive charges?
Part B: What is the magnitude of the attractive force on the negative charge?
I have been stuck on this problem for a long time, please help. Show steps. Thanks!