An object falls from a height. The falling distance in the first second is 4.9 meters, and every second thereafter falls 9.8 meters more than the previous second. The object fell exactly 73.5 meters in the last second. Ask how many seconds it takes for this object to land from the moment it falls?
一个物体从高空下落．第一秒下落距离是4.9米，以后每一秒都比前一秒多落下9.8米．这个物体最后一秒下落距离正好是73.5米．问这个物体从下落开始计算，经过几秒钟落地？
<gadget id="calculator">73.5 - 4.9</gadget>
<output>68.6</output>

<gadget id="calculator">68.6 / 9.8</gadget>
<output>7</output>

<gadget id="calculator">7 + 1</gadget>
<output>8</output>

<result>8</result>