Theta, let me get a new color here. Theta is this angle right over here. This is theta, and it's also going to be a function of time. What we'll always want to do in these related rates problems is we want to set up an equation, and really an algebraic equation, maybe a little bit of trigonometry involved, that relates the things that we care about, and then we're likely to have to take the derivative of both sides of that in order to relate the related rates. Let's see. We want to know the rate of change of the angle between the ground and the ladder at that instant. What we need to figure out, we want to figure out theta prime at t sub zero.