Two depots hold 180 and 250 tons; two customers order 200 and 150 tons. After the cheapest delivery plan, the tonnage left at depot D2 is:

1. The optimal plan sends 180 tons from D1 to C1 and nothing from D1 to C2. 2. C1 ordered 200 tons, so the remaining 20 tons come from D2. 3. C2's full order of 150 tons also comes from D2. 4. So D2 ships $20+150=170$ tons in total. 5. D2 started with 250 tons, leaving $250-170=80$ tons. _Source: NECTA ACSEE 2022 Advanced Mathematics 142/1, Question 3: Linear Programming_