Question

Given: Q1 = +20 µc = 2.0 x 10-5 C

Answer 1

The answer is:  [C]:  0.60 N  .
____________________________________________
Explanation:  
__________________________________________________________
We use the formula / equation for "Coulomb's Law"; 
      to get the answer, in "N", ("Newtons") : 
__________________________________________________________

    F  =   (k * q1 * q2) / r²  ;
__________________________________________________________
         and plug in our values that are given in the problem to solve:
__________________________________________________________

F  =   (k * q1 * q2) / r²  ;   (Plug in the values): to get: 

    =  { [(9.0 * 10⁹ N·m² ) / C² ] * (2.0 * 10⁻⁵ C) * (3.0 * 10⁻⁵ C) } / { (3.0 m)² } ;
__________________________________________________________
     =   {9.0 * 10⁹ * 2.0 * 10⁻⁵ * 3.0 * 10⁻⁵ } / { (3.0²) }  N ; 
________________________________________________________
   {Note: "N" is the value in "Newtons", which we want.
            The other units "cancel out" to "1".   
     Note that anything multiplied by "1" equals that same value.
     Note that anything divided by "1" equals that same value.}.  We shall retain the "2" significant figures in our final answer;
________________________________________________________
So we have:
_____________________________________________________
     F = {9.0 * 10⁹ * 2.0 * 10⁻⁵ * 3.0 * 10⁻⁵ } / { (3.0²) }  N  ;
_____________________________________________________
     F   =  (5.4 / 9.0)  N  ;
_____________________________________________________
     F = 0.60 N ; which is:  Answer choice: [C].
_____________________________________________________

Answer 2

6.7 x 10-11....Have a good day with a big fat A+