It takes 3 days for the ship to travel from A to B, and 4 days to travel from B to A. How many days does it take to float an unpowered raft from A to B?
船从A到达B要行3天，从B到达A要行4天．现在从A放一个无动力的木筏，飘到B需要几天？
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<gadget id="calculator">3 + 21</gadget>
<output>24</output>

<result>24</result>