The Attempt at a Solution
Using Coulomb's Law, here's what I've worked out:
Fx=0.309 - 0.593cos60°= 0.0125
√(0.01252 + 0.5142) = 0.514 N/C
and θ = tan-1(0.514/0.0125) = 88.6°
I'm not sure why webassign is telling me that my answer is wrong. I worked out a problem almost exactly like this with slightly different numbers and got it right...