Suppose a consumer has the utility function u(z1,z2) = z1 + z2 (a) in a well labelled diagram, illustrate the indifference curve which yields a utility level of 3.5. (b) if the consumer has income M and faces the prices p1 and p2 for z1 and z2, respectively, derive the demand functions for the two goods. (c) what types of preferences are associated with such a utility function