This question is so "stock" that it's easy to prepare for in advance. But it says more about a company that asks it than anything you design says about you. Clearly they haven't bothered to look into better ways of getting to know UX designers. It's not very analogous to their company either. A better one might be "how would you approach a project aimed at helping organic farmers get support from each other as well as share their research and expertise with new organic faming methods". The trick is NOT to jump right into designing on the whiteboard but to ask more questions about the goals for the project, especially the users, demographics, roles, but also the corporate timelines, the teams assigned to the project, and then suggest questions to research further, suggest site visits, etc. to show that you clearly understand the full UX process and you're not just a UI designer who creates in a vacuum to their own esthetics before understanding the purpose and context.