BSRM Ltd$.$ has two divisions: Steel Division $($upstream$)$: Produces steel rods at a variable cost of Tk$.50$ per unit, and it can sell them in the external market at Tk$.80$ per unit. Fabrication Division $($downstream$)$: Uses steel rods to manufacture construction components. It can purchase rods either from the Steel Division or from the open market at Tk$.80$ per unit. For the upcoming period, the Fabrication Division needs $10,000$ units of steel rods. The Steel Division has a production capacity of $50,000$ units, and the external demand is $45,000$ units. Requirements: a$)$ What is the minimum transfer price the Steel Division should charge? b$)$ What is the maximum transfer price the Fabrication Division should be willing to pay? c$)$ If the company$$s goal is to maximize overall profitability, what should the optimal transfer price be in this scenario? d$)$ Discuss one advantage and one disadvantage of using market$-$based transfer pricing in this context.