The velocity of the water is 5 kilometers per hour. Now it takes 6 hours for a boat to sail against the current in a 120-kilometer river, how many hours does it take to sail along the current?
水流速度每小时5千米．现在有一船逆水在120千米的河中航行需要6小时，顺水航行需几小时？
<gadget id="calculator">120 / 6</gadget>
<output>20</output>

<gadget id="calculator">20 + 5 + 5</gadget>
<output>30</output>

<gadget id="calculator">120 / 30</gadget>
<output>4</output>

<result>4</result>