It takes 2 hours for a ship to travel from A to B along the river. When returning, the speed of the ship in still water and current remains the same, and it takes 3 hours to travel from B to A. It is known that the distance between A and B is 120 kilometers, so how many kilometers per hour is the still water speed of the ship.
一条轮船从甲地到乙地是顺水航行，需要2小时到达，返航时轮船静水速度和水流速度都不变，从乙地到甲地需要3小时到达．已知甲、乙两地相距120千米，那么轮船的静水速度是每小时多少千米．
<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<gadget id="calculator">60 + 40</gadget>
<output>100</output>

<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<result>50</result>