It takes 4 days for a ship to go from city A to city B, and 5 days to go from city B to city A. Now put an unpowered raft from city A, how many days will it take to drift to city B?
轮船从A城到B城需要4天，从B城到A城需要5天，现在从A城放一个无动力的木筏，它漂流到B城需要多少天？
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 * 9</gadget>
<output>36</output>

<gadget id="calculator">4 + 36</gadget>
<output>40</output>

<result>40</result>