4.
when people decide what makes a fair trade, like exchanging 2 chickens for 2 sheep, they are

They are negotiating ! I hope I helped :)

Ifound this on google “that means that the graph of a function with direct variation has these features: it is a straight line: because the slope is the ratio y/x = k. it passes through the origin (0,0): because y = kx = k (0) = 0.” i hope this you for what your looking for