Growth rate of past 10 years and 5 years. See where it falls. Calculate it out to EPS in 5 and 10 years based on the performance. Multiply by avg P/E to get future potential price based on current/expected growth data. Discount the future price by whatever rate of return on investment you want/need, say 15% or 12.5% compound annual growth rate on investment over the given time frame. Simple.
Not sure what calculations inga is using for the $40 and change on Heinz. The growth rate on shareholder's equity alone make this deserving of a higher P/E than comparable food companies that are highly leveraged with little concern for intrinsic value of the company.