Let's ask this question step by step:
 Part A) 
 a x b = (3.0i + 5.0j) x (2.0i + 4.0j) = (12-10) k = 2k
 ab = (3.0i + 5.0j). (2.0i + 4.0j) = 6 + 20 = 26
 Part (c)
 (a + b) b = [(3.0i + 5.0j) + (2.0i + 4.0j)]. (2.0i + 4.0j) 
 (a + b) b = (5.0i + 9.0j). (2.0i + 4.0j)
 (a + b) b = 10 + 36
 (a + b) b = 46
 Part (d)
 comp (ba) = (a.b) / lbl
 a.b = (3.0i + 5.0j). (2.0i + 4.0j) = 6 + 20 = 26
 lbl = root ((2.0) ^ 2 + (4.0) ^ 2) = root (20)
 comp (ba) = 26 / root (20)
 answer
 2k
 26
 46
 26 / root (20)
        
             
        
        
        
Coulomb's law:
  Force = (<span>8.99×10⁹ N m² / C²<span>) · (charge₁) · (charge₂) / distance²
            = (</span></span><span>8.99×10⁹ N m² / C²<span>) (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. 
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