well i'm from Finland we use commas to show where decimals start. So the ansver is 695 miles and a bit more. It's dot in USA to show where decimals begin?
Since i already ansvered your planes i might do this aswell. General advice for all these, if you don't know what to do instantly draw a picture. Same cosine therom as in other one. Draw a picture into a triangle, have the starting point as origo and draw coordinate system...
F=(1/4pii*8.85419*10^-12F/m)*Q1Q2/r^2 Since the charges were same just opposite you can put Q1Q2 as Q^2. Solve Q. Then deduct from the ansver the charge there already is and divide by elementary charge.