Literally walked him through the steps of a DCF: Start with NI, add back Depreciation, add or subtract changes in working capital (asked how an increase in AR would affect it), subtract CapEx. Multiply the resulting yearly figures by the WACC (compounded yearly). Interviewer asked what I would do to the WACC if he asked me to manipulate the company's value to be lower. I responded that the WACC would need to be higher to give the company a lower value.