Question 1132969
You find that when you order 50 magnets, the average cost per magnet is $1.70 and when you order 75 magnets, the average cost per magnet is $1.40. What is the cost equation for these custom magnets? (Let x be the number of magnets.) 
=============
In the real world, the seller sets the price, and the buyer buys or not.
There might not be a "cost equation."