These mostly look like CFA leve 2 questions. I was able to answer them mostly in me head & out loud without any time constraint or pressure of the interview so take that into account. Under an interview scenario I think I would have had some difficulty on some.
1) It depends on the size of the investment as it pertains to company B. There different ways for accounting for a minority interest passive vs minority interest active, a controlling interest and a joint venture. The interviewer is asking about minority interest on the balance sheet which implies it's most likely accounted for using the full consolidation method. Companies must fully consolidate if company A owns more than 50% but less than 100% if company B. Assets and Liabilities are consolidated fully on the parent company and a line item titled minority interest is added to equity as a contra balance. Company A subtracts the percent not owned of company B's net assets.
2) The value of the investment in Nissan would fluctuate depending on the Yen's movement. Renault wouldn't mind if the Yen appreciated against the Euro, post investment, because that would increase the value of the investment when translated back to Renault's balance sheet. You would however protect against Yen depreciation using either a future or forward. You would (and this is where I would most likely slip up) sell Yen and Buy Euro's (please correct me if I'm wrong). If Renault guaranteed Nissan's debt then you would add that debt to Renault's balance sheet and from there you would have currency risk related to the Yen denominated debt. You would have interest rate risk if it was variable debt.
3) Increasing the depreciated life of assets will decrease the annual depreciation expense on the income statement. With a lower expense on the IS, you will then increase net income. On the cash flow statement you start with NI and add back depreciation so I don't believe changing the depreciated life of an asset would change the companies cash flows. Increasing AR days would imply a longer cash collection time, and therefore decrease cash flow from operation. Changes in AR aren't recorded on the income statement so NI would not change.
4) The unfunded pension liability is a real liability and should be on the balance already as a pension liability. You would want to know about the size of the asset and liability together with the size of the underfunded status. The bigger the asset base, the easier it would be to possibly earn $10m on those assets. Additionally you would want to know what rate of return and discount assumptions the company is using. Whether the plan is closed or open to new employees, and the age of the plan's participants. Also you would want to know whether the company's cash flows could sustain the negative cash flow's that would be required to fund the pension liability.
5) Duration is a bond's price change given a 1% up or down movement in interest rates, so in some ways it is a beta to the general interest rate. Bond's with a longer maturity typically have a higher duration than shorter term bonds.