From A to B, the uphill road accounts for (2/9), the flat road accounts for (4/9), and the rest are downhill roads. A car travels back and forth between A and B, traveling a total of 15 kilometers downhill. How many kilometers are there between A and B?
从甲地到乙地，上坡占(2/9)，平路占(4/9)，其余是下坡路．一辆汽车在甲乙两地间往返一趟，共行下坡路15千米．甲乙两地相距多少千米？
<gadget id="calculator">2 / 9</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 - (2/9) - (4/9)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/3) + (2/9)</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">15 / (5/9)</gadget>
<output>27</output>

<result>27</result>