Answer:
One important factor that Vivian needs to consider is that demand changes as a result of changes in price, however, other factors could affect the demand for goods or services, examples are, changes in the price of related goods, the income of the people, changes in preference etc.
Therefore, based on this fact, Vivian should consider "Price elasticity of demand." Price elasticity of demand can be defined as a measurement used in economics to show the responsiveness or elasticity of the quantity demanded of a good or service to a change in its price when nothing but the price changes.