Each of the eight sides of this stop sign is 12.5 inches long. How tall is the sign, from top to bottom? (It’s a regular octagon.)

Each of the eight sides of this stop sign is 12.5 inches long. How tall is the sign, from top to bottom? (It’s a regular octagon.)

The given answer is not the solution to this problem, “Height of Octagonal Stop Sign.” It looks like the answer provided is for an arithmetic sequence.