A building has 15 floors, each of which is the same height. The two went upstairs at the same time, and Xiaohu went upstairs twice as fast as Xiaoyun. When Xiaoyun reached the sixth floor, what floor did Xiaohu reach?
一座大楼共15层，每层一样高．两人同时上楼，小虎上楼的速度比小云快一倍，当小云到达第六层时，小虎到达第多少层．
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">10 + 1</gadget>
<output>11</output>

<result>11</result>