You and some friends take a hot-air balloon ride. One friend is late, so the balloon floats a couple of feet off the ground as you wait. Before this person arrives, the combined weight of the basket and people is 1220 kg, and the balloon, which contains 5980 kg of hot air, is neutrally buoyant. When the late arrival climbs up into the basket, the balloon begins to accelerate downward at 0.10 m/s2. What was the mass of the last person to climb aboard?