Why not write all of the numbers in decimal fraction form, to make them easier to compare?
68 2/3 = 68.666...
72 1/2 = 72.500
68 3/10 = 68.300
74 7/11 = 74.636...
68 1/2  = 68.500
550/8 = 68.750
Now ask yourself:  Which of the last four numbers is between 68.666.. and 72.500?
        
                    
             
        
        
        
A) 42,000m divided by 2 1/3 = 18,000m divide by 1000m to get km = 18km/hr
B) 18,000m divided by 60 to get minutes = 300m divide by 60 to get seconds = 5m/sec.
        
             
        
        
        
4 quarts are in a single gallon
        
                    
             
        
        
        
Answer:
the simplest way to finish your hw is to ask the Q of your hw here instead of asking us to help with your hw
 
        
                    
             
        
        
        
Last one i think 
x=0 or x=6