At least private property encourages ranchers not to over-graze when they aren't desperate. The incentive to produce on private plots is large, the incentive to produce on state-owned plots is small. Then draw a supply curve that intersects the demand curve at a low price. Intuitively, you need to think in terms of marginal analysis. Low prices of medicine mean large quantities of medicine demanded.
Demand exceeds supply.
There would be a shortage of 70 units. Supply exceeds demand. There would be a surplus of 100 units. The demand for large cars would increase - they are now cheaper to drive per mile. The demand for small cars would decrease, because people are shifting to larger cars instead.