Ou Ou, Xiao Mei, Koizumi, and Ao Zema still need to stay on the mountain to complete a week's survey mission (7 days). Each of them needs a bottle of water a day, but they only have 10 bottles of water left. It takes 2 days for a water deliveryman at the bottom of the mountain to bring at least as many bottles of water up the mountain as possible to solve the problem of water shortage.
欧欧、小美、小泉、奥斑马四人还需呆在山上完成一个星期的勘察任务(7天)，每人每天需要一瓶水，但他们只剩下10瓶水，而上山和下山各需2天，山下的一个送水员至少带多少瓶水上山，才正好解决缺水的困难．
<gadget id="calculator">7 + 2</gadget>
<output>9</output>

<gadget id="calculator">9 * 4 * 1</gadget>
<output>36</output>

<gadget id="calculator">36 - 10</gadget>
<output>26</output>

<gadget id="calculator">2 + 2</gadget>
<output>4</output>

<gadget id="calculator">4 * 1</gadget>
<output>4</output>

<gadget id="calculator">26 + 4</gadget>
<output>30</output>

<result>30</result>