Xiaohua and grandpa go upstairs at the same time, Xiaohua goes upstairs twice as fast as grandpa, when grandpa reaches the 4th floor, how many floors does Xiaohua reach.
小华和爷爷同时上楼，小华上楼的速度是爷爷的2倍，当爷爷到达4楼时，小华到了多少楼．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>