Explanation There are six possible combinations of changes in demand and supply when any of the two given events occur together. (i) The price of the music streaming service falls and the price of a wireless plan rises. Figure 1 shows the demand and supply curves of smartphones when the price of the music streaming service falls and the price of a wireless plan rises. The horizontal axis measures the quantity of smartphones and the vertical axis measures the price. The downward sloping curve marked D0 is the initial demand curve and the upward sloping curve marked S is the supply curve. The initial equilibrium is obtained at the point E. A fall in the price of the music streaming would lead to an increase in the demand for smartphones and this would shift the demand curve to D1. A rise in the price of the wireless plan would lead to a fall in the demand for smartphones and this would shift the demand curve to E2. The supply of smartphones remains unchanged due to these events. The magnitude of the change in demand and the final quantity of smartphones depend on the magnitude of fall in music streaming and rise in wireless plan. (ii) The price of music streaming service falls and more firms start producing smartphones. Figure 2 shows the demand and supply curves of smartphones when the price of the music streaming service falls and more firms start producing smartphones. The horizontal axis measures the quantity of smartphones and the vertical axis measures the price. The downward sloping curve marked D0 is the initial demand curve and the upward sloping curve marked S is the supply curve. The initial equilibrium is obtained at the point E. A fall in the price of the music streaming would lead to an increase in the demand for smartphones and this would shift the demand curve to D1. An increase in the number of firms producing the smartphones would increase the supply of smartphones in the market. This would shift the supply curve to the right to S1. An increase in the demand and increase in supply would definitely lead to an increase in the quantity and the change in price depend on the magnitude of change in demand and supply due to the fall in price of music streaming service and increase in production. (iii) The price of music streaming service falls and wages paid to workers increases. Figure 3 shows the demand and supply curves of smartphones when the price of the music streaming service falls and wages paid to workers increase. The horizontal axis measures the quantity of smartphones and the vertical axis measures the price. The downward sloping curve marked D0 is the initial demand curve and the upward sloping curve marked S is the supply curve. The initial equilibrium is obtained at the point E0. A fall in the price of the music streaming would lead to an increase in the demand for smartphones and this would shift the demand curve to D1. An increase in the wages of workers would lead to an increase in the cost of production and this would lead to a reduction in the supply of smartphones. The supply curve shifts to the left from S0 to S1. An increase in the demand and reduction in supply would clearly lead to an increase in the price of the smartphones and the change in quantity depend on the magnitude of change in demand and supply due to the fall in price of music streaming service and increase in wages. (iv) The price of wireless plans increases and the number of firms producing smartphones increases...