For a birthday gift, 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 while you wait. Before this person arrives, the combined mass of the basket and people is 1140 kg, and the balloon is neutrally buoyant. When the late arrival climbs up into the basket, the balloon begins to accelerate downward at 0.49 m/s22. What is the mass of the last person to climb aboard?