A road is 72 kilometers long. The ratio of the road that has been traveled to the remaining road is 4:5. How many kilometers are left to go?
一条公路长72千米，已经走的和剩下的比是4：5，还剩多少千米没走．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">72 * (5/9)</gadget>
<output>40</output>

<result>40</result>