The accepted sample totals are 12, 31 and 96, giving 139. Quantity zero is rejected. The member discount is a single 5-unit reduction, so three seats cost 3×12−5=31.

Critical check: Invalid quantities cannot produce a payable total and the membership discount is applied exactly once.

Final project: Deliver the calculator page, JavaScript, sample JSON, test results and README. Change the unit price to 15 in one named constant and update independent expected values while preserving the once-per-booking discount.