There are two boats, A and B. Ship A and the drifting object are traveling from the west of the river to the east at the same time, and boat B is also traveling from the east of the river to the west at the same time. Boat A travels for 4 hours and is 100 kilometers away from the drifting object. Boat B encounters the drifting object after traveling for 12 hours. The speed of the two boats is the same. How long is the river in kilometers?
有甲、乙两船，甲船和漂流物同时由河西向东而行，乙船也同时从河东向西而行．甲船行4小时后与漂流物相距100千米，乙船行12小时后与漂流物相遇，两船的划速相同，河长多少千米？
<gadget id="calculator">100 / 4</gadget>
<output>25</output>

<gadget id="calculator">25 * 12</gadget>
<output>300</output>

<result>300</result>