Answer:
You would need 2.5
Step-by-step explanation:
You can use a porportion to solve. 
 (cross multiply and solve)
 (cross multiply and solve) 
 
        
             
        
        
        
Answer:
7 balls
Step-by-step explanation:
Look for the worst case scenario:
Get 3 white, 2 green, and 1 black.
That adds up to: 3 + 2 + 1 = 6.
+1 red ball: 6 + 1 =7
7 balls
 
        
             
        
        
        
Please brainless if it’s wrong please message me