Now we're ready to optimize. To optimize, we just have to figure out what are the critical points here and whether those critical points are minimum or maximum value. So let's see what we can do. So to find a critical point, we take the derivative, figure out where the derivative is undefined equal to 0. And those are our candidate critical points. And then from the critical points we find, they might be minimum or maximum values. So the derivative of c of our cost with respect to x is going to be equal to 40 times x minus 180 times x to the negative 2 power.