A small boat sails 56 kilometers downstream and 20 kilometers upstream for the first time, and it takes 12 hours; the second time takes the same time to sail 40 kilometers downstream and 28 kilometers upstream. Find the speed of the boat in still water.
一只小船，第一次顺流航行56千米，逆流航行20千米，共用12小时；第二次用同样的时间，顺流航行40千米，逆流航行28千米．求这只小船在静水中的速度．
<gadget id="calculator">56 - 40</gadget>
<output>16</output>

<gadget id="calculator">28 - 20</gadget>
<output>8</output>

<gadget id="calculator">16 / 8</gadget>
<output>2</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">56 + 40</gadget>
<output>96</output>

<gadget id="calculator">96 / 12</gadget>
<output>8</output>

<gadget id="calculator">56 / 8</gadget>
<output>7</output>

<gadget id="calculator">12 - 7</gadget>
<output>5</output>

<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">8 + 4</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<result>6</result>