The proceeds of disposition is usually the amount you received or will receive for your property. In most cases, it refers to the sale price of the property. When you trade in a property to buy a new one, your proceeds of disposition is the amount you receive for the trade-in.

So in this case proceeds is 60k?

Proceeds (what you received) =  sold for 100k minus closing costs of 40k = 60K .  Is this the amount (60K) you used in the proceeds?