An object falls from a high altitude, and after 4 seconds, it is known that the falling distance in the first second is 4.9 meters, and the falling distance in each second is 9.8 meters more than the previous second. How far was the object from the ground before it fell?
一个物体从高空下落，经过4秒钟落地，已知第一秒钟下落的距离是4.9米，以后每秒钟下落的距离比前一秒钟多9.8米．这个物体下落前距地面多少米？
<gadget id="calculator">4.9 * 4</gadget>
<output>19.6</output>

<gadget id="calculator">9.8 * 6</gadget>
<output>58.8</output>

<gadget id="calculator">19.6 + 58.8</gadget>
<output>78.4</output>

<result>78.4</result>