Owl: A circular oil patch on calm water expands as emergency crews watch. When the radius is 12 meters, it's growing at 0.4 meters per minute. How fast is the area growing at that moment?
Related rates problems share a rhythm: draw and label, write a geometric or physical constraint, differentiate with respect to time, then plug in the known rates and the instant's values.
The classic self-own: plugging the numbers before you differentiate, which freezes quantities that are still changing.
On the board: A = πr². Before any algebra, which quantities are functions of time here?