two charged objects carry a negative charge of 2*10c. calculate their distance apart if the force between them is 10n
I think you may have left out a negative exponent of 10. Otherwise the charge is 20 C. That is a lot of charge.
Call the charge Q, whatever it is.
The force between the objects is
F = k Q^2/d^2 = 10 Newtons
where k is the Coulomb constant
8.99*10^9 N m^2/C^2
and d is the separation distance in meters.
Solve for d