minimize or maximize? subject to? optimum function? and plot the corner points for the feasible area

The Sweet Smell Fertilizer Company markets bags of manure labeled "not less than 50 lb dry weight." The packaged manure is a combination of compost and sewage wastes. To provide good-quality fertilizer, each bag should contain at least 35 lb of compost but no more than 45 lb of sewage. Each pound of compost costs Sweet Smell 5 and each pound of sewage costs 4. The aim of the objective function for the Sweet Smell Fertilizer Company should be to the objective value