. An economist investigating the tea market assumes that Q _t = f(P _t , Y,A,N, P _c ) where Q _t is the quantity of tea demanded, P _t is the price of tea, Y is the average household income, A is the advertising expenditure on tea, N is the population and _Pc is the price of coffee.

(a) What does Qt = f(Pt, Y,A,N, Pc) mean in words?

(b) Identify the dependent and independent variables.

(c) Invent a specific form for this function. (Use your knowledge of economics to deduce whether the coefficients of the different independent variables should be positive or negative.)