Surely, if you have a question like that, you know the basic formulas.

The y-coordinate of the centroid of a region (center of mass assuming uniform density) is

.

is, of course, the area of the region.

Once, when I was teaching this, a student became fascinated by the word "lamina" (had never seen it before, apparently). As the last question on the final exam, I asked "What is 'lamina' spelled backwards?"

Another student became furious with me because "That question doesn't make any sense!"