Im doing online homework of consumer surpluses and the example gives a step that is the integration part that I don't understand. it goes from squareroot(81-.1q) -8 dq and this is what you get when you integrate -20/3 (81-.1q) ^3/2 -8q My question is how do you get the -20/3 in front? Where does that come from? Hopefully you understand the different steps.