please answer it to the point in 50 minutes

it is a complete statement , answer it

The graph in Figure 1 below is the output of a distillation column optimisation study. Review the graph and answer the following questions: i. What is the approximate optimum column design based on the data in Figure 1? Justify your answer. [3 marks] ii. What impact would you expect an increase in the operating costs to have on the optimised solution? Explain your answer. [3 marks] iii. Explain the method that would have been used to obtain each point on the graph. [3 marks]