1. The problem statement, all variables and given/known data Find the electric field strength at point P, which is located midway between charges A and B. The charges are separated by 20 cm. The first charge has a charge of 20 micro coulombs. The second charge has a charge of -30 micro coulombs. 2. Relevant equations Electric field strength E=Kq/r K is coulomb's constant 9x10 raised to the ninth power. Q is charge. Ris distance from charge. 3. The attempt at a solution I'm not sure where to start. You need the charge at point P to use Coulomb's law.