The fuel carried by a ship can be used for up to 16 hours. When sailing out against the current, the speed is 42 kilometers per hour, which is (7/9) of the speed when returning. How long does it take for the ship to sail at most before returning? (Solve with ratio)
一艘轮船所带的燃料最多可以用16小时，驶出时逆水，速度是每小时42千米，是返回时速度的(7/9)，这艘轮船最多驶出多长时间就应返回？(用比例解)
<gadget id="calculator">16 * 42</gadget>
<output>672</output>

<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">42 / (7/9)</gadget>
<output>54</output>

<gadget id="calculator">672 / 54</gadget>
<output>112/9 = around 12.444444</output>

<result>112/9 = around 12.444444</result>