Darnel needs to spend three days making jam if he wants to jar 15 liters.
Explanation:
If you are to assume the relationship is proportional then if he makes 10 liters in 2 days you divide 10 by 2 and you get 5. This means he makes 5 liters a day. Then you add 5 to 10 and you get 15 which means you are adding another day(5) So he needs to work an extra day which would give you three dyas total. Hope this helped!