Two 4.0 kg masses are 1.0 m apart on a frictionless table. each has 1.0 μc of charge. what is the magnitude of the electric force on one of the masses?

Coulomb's law:

  Force = (8.99×10⁹ N m² / C²) · (charge₁) · (charge₂) / distance²

            = (8.99×10⁹ N m² / C²) (1 x 10⁻⁶ C) (1 x 10⁻⁶ C)  / (1.0 m)²

            = (8.99×10⁹ x 1×10⁻¹² / 1.0)  N

            =      8.99×10⁻³  N

            =        0.00899 N repelling.

Notice that there's a lot of information in the question that you don't need.
It's only there to distract you, confuse you, and see whether you know
what to ignore.

-- '4.0 kg masses';  don't need it. 
   Mass has no effect on the electric force between them.

-- 'frictionless table';  don't need it.
   Friction has no effect on the force between them,
only on how they move in response to the force.