[proteal]

If you are a monopoly producer (which seems fair in this context) you would set the price of the rocks where your marginal revenue equals your marginal demand. Loosely, you’d do a market survey to see what price the market would be willing to pay for a mars rock[0], then figure out your cost structure for bringing back one more kilo of rocks. You’d factor in cost to launch a rocket, fuel for the rocket, astronaut salaries, and don’t forget terrestrial costs like marketing and distribution! If you did a good enough job at predicting supply and demand, you wouldn’t actually care what the price of the product is because you would have claimed all the consumer surplus for yourself :)

To specifically answer the optimal quantity question, the above answer implies that you would keep bringing rocks home until the cost to bring them back is higher than the price you set. To be clear, you could still go out and get more rocks and sell them for less and still make a profit, but you wouldn’t maximize your profit with that strategy. Competitive markets nudge behavior towards providing more product for less profit/cost which is why we love competition.

[0] Planet money did a great podcast on how to actually do this. Here’s a link to a transcript (though listening is probably best): https://podscripts.co/podcasts/planet-money/how-much-for-tha...