I am trying to figure out a formula to determine the value of an item with an unknown amount of platinum, palladium, and rhodium in it. I have previous values and the dates of those values. I want to figure out a formula with multiple values on multiple dates and the prices of those metals on those dates, based on the change of value of the item compared to the value of those 3 metals, to then be able to input the current value of the 3 metals and get the current value of the item. Hopefully that made sense. Basically a formula that can determine the amount of metals in the item based on the change of 3 variables at different times. Thank you for any help.