A heptagon is a seven-sided polygon. What is the greatest number of the following properties that a single heptagon can possibly possess?
- Its interior angles add up to $900$ degrees
- It has exactly four acute interior angles.
- It has no obtuse interior angles.
- All its sides are equal.
- It has exactly one line of symmetry.
If you liked this problem, here is an NRICH task
which challenges you to use similar mathematical ideas.