A building has 19 floors, and the number of steps between every two floors is the same. It is known that A goes upstairs twice as fast as B. When B reaches the 6th floor, what floor is A on?
一座大楼共有19层楼，每两层楼间阶梯数都相同．已知甲上楼的速度比乙快一倍，当乙达到第6层楼时，甲在第多少层．
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

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

<result>11</result>