
Hope you could get an idea from here.
Doubt clarification- use comment section.
 
        
             
        
        
        
Answer:
80 students
Step-by-step explanation:
12/80 is 0.15 or 15%
 
        
             
        
        
        
1/9 of total marbles = 1/9 × 36 = 4
so Alexis gave 4 marbles to Sara. 
And so Alexis is left behind with 32 (36-4) marbles and so Sara have 4 marbles now
        
                    
             
        
        
        
Answer:
Step-by-step explanation:
At the first place is better because
$0.8 * 5 = $ 4
$4.5 / 5 = $0.9
Is more expensive in the another place