Two polystyrene balls, one has a charge twice the amount than the other..find charges

MissJewels

1. The problem statement, all variables and given/known data
Two balls of polystyrene foam are about 4 cm from each other and repel with an electric force of 0.2 N. Find the values of the two charges knowing that one of the balls has a charge that is twice the other.


2. Relevant equations
F= (kq1q2)/r²


3. The attempt at a solution
F= (k·Q·2Q)/r²
0,2 = ( 9x10⁹·2Q² ) / (0,04)²

Q= +1,77 x 10^-14


AND its wrong! The right answers should be :
(+or-)188nC, (+or-)267nC