The NEM Problem
Imagine you sit in a cave with both iron ore and coal to harvest inside. You and your friend start harvesting at the same time. There are two bags, one with iron ore and the other one with coal. At some point you will look into the bags and count.
The easiest thing to do would be to bring both bags together into one and start mixing. But here begins the problem. Your inventory is empty half of the time. Now think about this: Each time you walk you take as much iron ore to the coal and as much coal to the iron ore as you can carry. In the end, the right amount of ingredients has to be in the bags. You also want to bring Fire Essences and food to both bags.
In addition, every time you walk between storage and iron or storage and coal you pick up some ingredient from that location. The question is, how much iron ore and coal needs to be harvested in each place ? Let the carry capacity of the mule be variable.