Closing time in a deliberately simplified traffic model

A fictional classroom display places two aircraft on directly opposing straight tracks at the same constant altitude. Initial distance is 35 nautical miles. Their groundspeeds are 180 and 240 knots, and the exercise assumes no turns, acceleration, wind change or communication delay. A learner calculates a meeting time and proposes using that time as the latest safe moment to begin coordination. Another distinguishes the mathematical intersection from an approved separation arrangement. The worksheet provides no actual airspace, protected minimum, surveillance eligibility, controller authorization or aircraft maneuvering capability. The task asks for the arithmetic and the limits of its interpretation. A sound answer identifies relative speed and unit conversion while explicitly rejecting the idea that an ideal meeting-time calculation authorizes a real clearance or a delay in protecting traffic.