If you have sold 12 items in 7 weeks, thats to say 1.71 items pr. week
how do you convert that to % sold pr. week ?
and then convert that into a excel friendly code
I dont know but, if you wanted to know the % amount of stock you've sold you would need the amount of Total stock you have to take away from right?
so if you had 120 items in stock and you sold 12 items in a week, that would be 10% of stock sold per week right ?
Wrong, that's not the question. You're missing a value - how many items do I have in stock.
So you have your values as a function of time - just stick in t=3 for item A and equate it to your function for B.