I think it should be x(ax +b) + c. Not sure though.
        
             
        
        
        
The area equation is 

, which when solved equals 50.24.  That's the third answer on your list.   
 
        
        
        
2 is one, i really don’t remember this. I think 6 and 4 3 i think.
        
             
        
        
        
0.8
you find how much he needed so:
24*0.3=7.2
than 8 he had , so whats left over
8-7.2=0.8