Interview Question - If you were to value a public company...

private company you would value based on comps if you have no data on their cash flows

you can project the numbers based on different economic factors and previous growth rates and expected industry growth rates

The best answer I can think of is to look at comparable companies as ivey_ib said. During a few of my interviews I was asked this question. Every time I gave an answer (eg: look at comparable companies, value individual assets owned by the company...etc.) I was told there is no relevant information that would give me any useful data. My opinion is that there really is not correct answer (in my situation); I think they are just looking to see how you would employ each of the alternative valuation techniques available to you. They just want to see if you know the techniques basically. Best bet is to show them you are familiar with each technique.