Seems like a wordplay question.
A "scale" is used for measuring length.
A different sort of "scale" is used for measuring mass.
        
             
        
        
        
Answer:
Step-by-step explanation:
So the distance that he ran is 30 yards since he ran from the 10 to 40 yard line. making it 30 yards. It is then said he ran this in 10 seconds
Now all you have to do is divide 30yards by 10seconds to see how many yards he ran in a sec. Dividing it you get 3 yards per second
 
        
             
        
        
        
Answer:
-1
Step-by-step explanation:
slope=(y2-y1)/(x2-x1)=(2-4)/(0+2)=-2/2=-1
 
        
                    
             
        
        
        
Answer:
-2.6
Step-by-step explanation:
Basically you just subtract 7.1 from 5.7 which will give you -2.6 I don't really know how to explain it much more
 
        
                    
             
        
        
        
Answer:65
Step-by-step explanation:
I'm not sure what you mean by "expression form," but if its simpliest form, you would simply do 20+5*9, and 5*9 is 45. 45+20 is 65