Ok, here is what I have. See attachment to complete the problem. What is the magnitude of force exerted on charge q1 by charge q3 and horizontal component of force exerted? Formula: q1q2 / 4piEor^2 Part 1) (4*10^-6)(2.12*10^-6) / 12.56 (8.85*10^-12)(1*10^-2) = 7.628917917176 N or Rounded off as 7.63N Part 2) 7.63 N sin 135 degrees = 5.39 N Now I understand the above, howver what I can understand is the following. The resultant force exerted on the charge q1 by the other 3 charges is what? But what if we replaced q1 with charge -4*10^-6, what resultant force would be exerted by the other 3 charges?