How do you do this math problem?

The cost of production of a commodity is $12 less per unit at a point A than it is at a point B, and the distance between A and B is 100km. uming that the route of delivery of the commodity is along a straight line, and that the delivery cost is 20 cents per unit per kilometer, find the curve at any point of which the commodity can be supplied from either A or B at the same total cost.