An apartment complex included a fixed price of water in the monthly rent. One day, the city decided to attach a water meter to each individual apartment and charge the tenant for actual water usage. As a result, water usage in the apartment complex went way down. Explain this situation using a principle of economics (10 points)

Four key marketing decision variables are price (p), advertising (a), transportation (t), and product quality (q). consumer demand (d) is influenced by these variables. the simplest model for describing demand in terms of these variables is: d = k – pp + aa + tt + qq where k, p, a, t, and q are constants. discuss the assumptions of this model. specifically, how does each variable affect demand? how do the variables influence each other? what limitations might this model have? how can it be improved?