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 as you wait. Before this person arrives the combined weight of the basket and people is 1400 kg, and the balloon is neutrally buoyant. When the late arrival climbs up into the basket, the balloon begins to accelerate downward at 0.61 m/s2. What was the mass of the last person to climb aboard?

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