The demand for coffee, Q, in pounds sold per week, is a function of the price of coffee, c, in dollars per pound and the price of tea, t, in dollars per pound, so Q = f(c, t)

a. Do you expect fc to be positive or negative? What about ft? Explain.
b. Interpret each of the following statements in terms of the demand for coffee: f(3,2) = 780 fc(3,2) = −60 ft(3,2) = 20