The Milton Lumber Company sells boards of various lengths (4-foot, and 7-foot wood boards). This company's customers' demand is 25 for 4-foot boards, and 40 for 7-foot boards per week. Milton Lumber cuts up boards of 20 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.

1. Define the decision variables
2. Define the objective function
3. Define the constraints
4. Determine an optimal solution.