6. Suppose hamburgers and tacos are substitutes. A rise in the price of tacos causes the demand for hamburgers to increase, leading to a rightward shift of the demand curve, resulting in an increase in the equilibrium price and quantity. 7. Assume that income falls and hamburgers are inferior goods. Then a fall in income leads to the following movement in the demand-supply graph of hamburgers. Price of hamburger D- Quantity of hamburgers