The correct answer that i came up with is D
        
             
        
        
        
70 = 50 * x/100
x = 70/50*100 = 140
Seventh is 140% of 50.
        
             
        
        
        
My guess is 9 hours, because since pipe a takes 12 hours and with pipe b it takes 9, it's 12-9=3
I think.
        
             
        
        
        
The other 6 books can be arranged in 6 ways
= 6*5*4*3*2*1 =  720 ways  answer
        
             
        
        
        
Answer:
If the total perimeter of square is 48 cm, then the length of one side is equal to 48 divided by 4, since all sides of a square are the same.
So, the correct answer is 12. 
Let me know if this helps!