The Milton Lumber Company sells boards of various lengths ( 4 -foot, 7 -foot, and 10 -foot wood boards). This company's customers' demand is 20 for 4 -foot boards, 40 for 7 -foot boards, and 3010 -foot boards per week. Milton Lumber cuts up boards 21 feet in length to meet this demand and wants to determine how to satisfy its customers' demands with a minimal amount of waste. Assume that all boards share the same width and thickness. Formulate and solve an IP model. a) Define the decision variables b) Define the objective function c) Define the constraints d) Determine an optimal solution