A local power company is considering increasing its generating capacity to meet expected demand over the next 5 years. Currently, the company has a generating capacity of 600MW. As per the demand forecast, the minimum generating capacities required over the next 5 years are as follows: The company can increase its transmission capacity by purchasing five different types of generators: 20,50,80, 100 , and 120MW. The costs of acquiring, installing, and operating each of the five types of generators are summarized below: Any number of generators (of any type) can be added in any year. However, once a generator is added, it must be operated in the future years as required. Formulate a mathematical programming model to determine the least cost expansion plan, for 5 years, while fulfilling all yearly demand