Final answer:
The demand for coffee in Mina's case is elastic because the quantity demanded increases significantly when the price is lowered. Despite coffee generally having an inelastic demand, Mina will get bigger revenue at the lower price of $15, as the increase in quantity demanded outweighs the decrease in price.
Step-by-step explanation:
The student is asking whether the demand for coffee is elastic or inelastic based on the change in quantity demanded when the price changes. If Mina sells coffee for $20 per pack, the quantity demanded is 200 packs, and when she lowers the price to $15, the quantity demanded increases, this suggests the demand for coffee is elastic. There's greater change in quantity demanded relative to the change in price.
Considering an elasticity of demand for coffee of about 0.3, which indicates a 10% rise in the price would lead to a 3% drop in the quantity demanded, we find the demand for coffee to be inelastic. However, for Mina's specific situation, because there's a considerable increase in quantity demanded when lowering the price, her revenue will be bigger at the lower price of $15. Thus, the correct answer is c. Elastic; $15.