Two tiny conducting spheres are identical and carry charges of -21.0 µc and 47.5 µc. they are separated by a distance of 2.39 cm. (a) what is the magnitude of the force that each sphere experiences, and is the force attractive or repulsive

The force is given by this equation

F =   k *q1*q2
        
             r^2

where K is Coulomb's constant = 9.10^ 9 [N.m^2 /C^2]

q1 is the value of charge 1, q2 the value of charge 2 

r is the distance between them

F = 9*10^9 * -21.10^-6 * 47.5 10^-6 
      = -15716,636 N (Negative so it is Attractive                                                                                                                            Force)
                       (0.0239)^2