Last night I dreamt I was a high school geometry teacher, and offered my class an A if they solved a story problem with no clues, B if with one clue, and C if two clues.

I have a straight iron bar (I clearly tell them it’s exact length). I bend it into a perfect circle. I cut it to make two matching semicircles. I lean them up together to make a four-footed arch (I clearly explain that the semicircles only touch at their exact tops). I give them the distance between the opposing feet of the arch. I ask them to solve for the height of the arch.

Question: what are the two clues?