Hint: if you add the gold (from selling stuff you do not need and what you already have) together with the value of the items you want to keep, and then divide by four, things will make a bit more sense.
So,that's 5,000gp in addition to whatever his share of the current division is. Emagor is definitely interested in the Ring of Wizardry . Now what is the total value of one share from which the price of the ring is to be deducted?