A truck delivers goods from place A to place B, which is 315km away. It is known that 135 km has been traveled in the first 3 hours. If the rest of the distance is completed at the same speed, how many hours will it take? (Solve with ratio)
一辆货车从甲地去相距315km的乙地送货．已知前3小时行了135km，如果用同样的速度行完剩下的路程，还要行几小时？(用比例解)
<gadget id="calculator">315 - 135</gadget>
<output>180</output>

<gadget id="calculator">180 * 3</gadget>
<output>540</output>

<gadget id="calculator">540 / 135</gadget>
<output>4</output>

<result>4</result>