There is a tall building, it takes 2 minutes to go up a floor, and 1 minute and 30 seconds to go down a floor. Xiao Ming lives on the ground floor. He starts to send letters from the bottom floor to Mr. Wang who lives on the top floor at 12:25. After 1 minute, immediately return to the home on the ground floor. The time is 13:15. How many floors does this tall building have?
有一高楼，每上一层楼需2分钟，每下一层楼需1分30秒，小明家住底层，他从底层于12点25分开始上楼送信给住最高层的王老师，交信时用了1分钟，立即返回底层家中，此时时间是13点15分，这座高楼一共有多少层．
<gadget id="calculator">50 - 1</gadget>
<output>49</output>

<gadget id="calculator">2 + 1.5</gadget>
<output>3.5</output>

<gadget id="calculator">49 / 3.5</gadget>
<output>14</output>

<gadget id="calculator">14 + 1</gadget>
<output>15</output>

<result>15</result>