John D. Rockefeller (2015). “John D. Rockefeller on Making Money: Advice and Words of Wisdom on Building and Sharing Wealth”, p.17, Skyhorse Publishing, Inc.
John D. Rockefeller (2015). “John D. Rockefeller on Making Money: Advice and Words of Wisdom on Building and Sharing Wealth”, p.23, Skyhorse Publishing, Inc.