The opposite of something means to change this signed that is with the number. 
If it is a positive number, the opposite would be negative.
 So in this example, if it's the opposite of positive 5, that is -5. The opposite of -5 would be positive 5.
 The equation that shows this correctly would be D.
        
             
        
        
        
Given, distance between South Carolina and Texas = 
Distance between Texas and California = 
Let's assume, both the distance is same. 

=> 
=> 
=>
Plug x = 113 in 
 Miles.
 Miles.
Similarly,  miles
 miles 
Since 2500 divided by 2 = 1250 miles, hence our assumption was correct, Texas lies between both the cities. 
 
        
                    
             
        
        
        
First, subtract k from both sides. That means c - k is in the left side and 3x is on the right. Then, divide by 3 on both sides. So, the answer is x = (c - k) / 3.