@last sentence: the net worth the value of everything in the world or of that item
@second last sentence: the mathematical operation is solving the worth of that item, and in this case the better computer is worth 6 moneys, because its price is 13 monies.
@third sentence: the price that you set for the better computer, which is 13.
so if you assign the better computer a value of 6, then the value of the world is 156, so the current money is now worth 4% more than it was before the better computer existed.