This answer would be 21 because you’d just do 15 increased by 40% which gave me 21
Answer:
Option D. 
Step-by-step explanation:
Let
x------>the greatest possible value
we know that
If four people write the number zero, then the average will be

I believe its the second one because it say four times the number wich the number is the y and it is = too the number wich is y and increased going up are adding by 9. hope that helped.