If you read the details in some of the "correct" answers[1], they are not actually correct. The model used an assumption that the width is equal to the thickness, which is not given in the problem. The width is cancelled out in the end, so the resulting number is correct, but a math teacher would label such answers wrong.
[1] Text prompt only, run 2; prompt and image, run 3.
[1] Text prompt only, run 2; prompt and image, run 3.