<em>so</em><em> </em><em>the</em><em> </em><em>answer</em><em> </em><em>is</em><em> </em><em>of</em><em> </em><em>option</em><em> </em><em>C</em><em>.</em><em>.</em><em>.</em><em>.</em>
 
        
                    
             
        
        
        
13, because 78 postcards divided by 6 cards per board = 13 poster boards 
        
             
        
        
        
Answer:
_<u>7</u> + 3 = 3 + 7 : commutative property,[if something is added or subtracted]
0 +<u>5</u> _ = 5 is it: identity property.[if 0 is added or subtracted]
2 + (6 + 8) =(2 + 6)+ _<u>8</u> associated property
[if added or multiplied]