Boost converter duty: PE Power Power Electronics practice question

A rooftop PV string feeds the boost (step-up) stage of a string inverter, which regulates a 380 V dc link. The string's open-circuit voltage is 260 V, and the maximum-power-point tracker holds the string at 200 V. Treating the boost converter as ideal and in continuous conduction, the switch duty cycle at the maximum power point is most nearly: