An object falls from a height of 180 meters. It falls 5 meters in the first second, and 15 meters in the second second. The last second always falls 10 meters more than the first second. How long does it take for this object to hit the ground?
一个物体从180米的高空落下，第1秒内它落下5米，第2秒内它落下15米，…后1秒总比前1秒多下落10米．这个物体约多少时间就可以落到地面？
<result>6</result>