It was 9. It was a regular polygon (equal sides and equal angles) and each angle was 40 degrees.

360 / 40 = 9.

It's a test to see if you can take established principles and apply logic to them. It's not a test of memorization, which is why they give you the properties of a triangle (like having a total of 180 degrees).

He seems overly hostile. The 'arbitrary' rules have well thought out reasoning behind them.

For example, he gets sarcastic and puts 4 question marks behind the rule that wrong answers are weighted at 1/4 of a point, but that rule is actually benign. It punishes random guessing but rewards an intelligent guess. The rule exists to be fair to you.

The test presents its rules upfront so that you don't get snared by obscure rules. The test gives you reference material (like the Pythagorean Theorem and the volume of a cylinder) because it's about ability, not arbitrary memorization.