Someone goes to the 15th floor of a business building. There is no elevator below the 4th floor (the 4th floor can take the elevator). It takes him 30 seconds to walk from the 1st floor to the 2nd floor, and the elevator speed is 10 times faster than walking. May I ask: How many seconds does it take him to reach the 15th floor?
某人去一座商务楼的15层，4楼以下不设电梯(4楼可乘电梯)，他从1楼步行到2楼用了30秒，电梯速度是步行的10倍．请问：他到达15楼共需多少秒．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">30 / 1</gadget>
<output>30</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<gadget id="calculator">30 / 1 / 10</gadget>
<output>3</output>

<gadget id="calculator">15 - 4</gadget>
<output>11</output>

<gadget id="calculator">3 * 11</gadget>
<output>33</output>

<gadget id="calculator">90 + 33</gadget>
<output>123</output>

<result>123</result>