Mark has 32 marbles and John has 96 marbles. If you add the marbles together they both have a total of 128.
        
                    
             
        
        
        
   You should be able to set up a proportion between the sides something like (18+x)/x=(56+21)/56
 
        
             
        
        
        
To determine the percent change in price, solve for the differences between the original prices and the sale prices. Then, divide the difference by the original price and multiply by 100%.
Guitar 1:       (($160 - $100) / $160) x 100% = 37.5%
Guitar 2:       (($250 - $150) / $250) x 100% = 40%
Thus, guitar 2 has a greater percent change in price.
        
                    
             
        
        
        
2 x 10 to the 3rd power is 
 2x10^3
        
             
        
        
        
It is 39..................................