boat was going upstream, and someone on the boat lost the kettle under the bridge and was washed away by the water. When the boat turned back, 20 minutes had passed. Later, at the downstream of the bridge, 2 kilometers away from the bridge, he chased Kettle. So what is the speed of the river in kilometers per hour?
一船逆水而上，船上某人于大桥下面将水壶遗失被水冲走，当船回头时，时间已过20分钟．后来在大桥下游距离大桥2千米处追到了水壶．那么该河流速是每小时多少千米？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">2 / (2/3)</gadget>
<output>3</output>

<result>3</result>