The ball is thrown straight up at $12 \mathrm{~m} / \mathrm{s}$ relative to the balloon, which is already rising at $10 \mathrm{~m} / \mathrm{s}$. So, the ball's initial velocity relative to the ground is the sum of these two velocities: $10 + 12 = 22 \mathrm{~m}
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