In a building, it took 6 seconds for Naughty to go from the 1st floor to the 2nd floor, 13 seconds from the 1st floor to the 3rd floor, 21 seconds from the 1st floor to the 4th floor, and 21 seconds from the 1st floor to the 4th floor. It took 30 seconds to reach the 5th floor. According to this rule, how many seconds did it take to go from the 1st floor to the 6th floor.
在一栋楼房里，淘气从1层上到2层用了6秒钟，从1层上到3层用了13秒钟，从1层上到4层用了21秒钟，从1层上到5层用了30秒钟，按照这个规律，从1层上到6层用了多少秒钟．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">30 / 4</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">(15/2) + 0.5</gadget>
<output>8</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">6 / 1</gadget>
<output>6</output>

<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">8 * 5</gadget>
<output>40</output>

<result>40</result>