Online derivative calculator:
https://www.derivative-calculator.net
https://www.symbolab.com/solver/derivative-calculator
General directories and indexes of economic information are:
The Library of Economic and Liberty: https://www.econlib.org/
Market conditions and prices for coffee are found in:
http://www.ico.org/coffee_prices.asp
For agricultural policies in OECD countries, see:
http://www.oecd.org/dataoecd/34/35/43247947.pdf
Information on tax rates in the various states of the United States is found in:
http://www.taxadmin.org/fta/rate/tax_stru.html
For rent control, see:
http://meganmcardle.theatlantic.com/archives/2009/10/
https://www1.nyc.gov/site/rentguidelinesboard/resources/rent-stabilized-building-lists.page
http://www.econlib.org/library/Enc/RentControl.html
Data on the International transactions of the United States are found in:
Bureau of Economic Analysis web site: http://bea.gov/ and clicking "international data."
Federal Reserve Bank of St. Louis: https://fred.stlouisfed.org/