After driving 210km from place A to place B, the car is still 30% away from place B. How many kilometers are there between places A and B?
从甲地到乙地汽车行驶了210km后离乙地还有30%没有行完，甲乙两地相距多少km．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">210 / (7/10)</gadget>
<output>300</output>

<result>300</result>