Answer:
209.53 N
Explanation:
To find the force on the third charge you use the Coulomb formula:
k: Coulomb's constant = 8.98*10^9 Nm^2/C^2
The force on the third charge is the contribution of the force between the third charge and the other ones:
By taking into account that the third charge is at the middle of the distance between charge 1 and charge 2 you have r = 0.12m/2 = 0.06m
Furthermore, you take into account that the first charge repels the third charge and the second charge attracts the third charge.
By replacing you have:
Hence, the force between on the third charge is 209.53 N