Valuing a business is not an exact science or art. It relies on applying a commercial view of the macro-economic marketplace to a specific industry and business, understanding the numerical trends and applying a discount for the risk.
Many people mistakenly think that the value of a business is solely in the balance sheet, but it is important to remember that the aim of a valuation is to ascertain its worth as an investment purchase either to sell on, combine with another asset or as a standalone asset paying future dividends. In practice it is often a combination of each of these.