In economics, if one is producing a certain quantity of things, the "**marginal cost**" is defined to be the cost of producing one additional item. This can vary, depending on how many items you've created. The marginal cost of creating one widget, for example, could be the cost of the entire factory you set up to create it, but the marginal cost of the $1{,}000{,}000$th widget might be just a few cents. Let's say you are producing detergent, and the cost, in dollars, of producing $x$ gallons of detergent is given by some function $C(x)$. Which of these values will likely give a good approximation of the marginal cost of producing $0.01$ more gallon after $g$ gallons have already been produced? [[☃ radio 1]]