Answer:7881 years
Step-by-step explanation:
You can use the equation
fraction remaining = 0.5n where n is # of half lives elapsed 
n = ?
fraction remaining = 1 - 0.612 = 0.388
0.388 = 0.5n
n = 1.37 = the # of half lives
1.37 x 5750 yrs = 7881 years
 
        
             
        
        
        
Answer:
100-x
Step-by-step explanation:
Hope this helps:) 
 
        
             
        
        
        
Answer:
x=11
Step-by-step explanation:
You do 38/3x+3 and 19/x+7 and then cross mulitply and get 57x+57=38x+266. Then yoy subtract 57 from 266 and get 57x=38x+209. Now you have to subtract 38 from 57 and then answer will be 19. So now you have 19x=209. Finally you divide 209 by 19 and get x=11. Good luck!