ship travels from port A to port B at a speed of 25 km/h, and from port B to port A at a speed of 15 km/h. The round trip takes 4 hours. How many kilometers is the voyage between port A and port B? (column equation solution)
轮船从甲港到乙港，速度为25千米/时，从乙港到甲港，速度为15千米/时，往返一次共航行4小时．甲、乙两港的航程是多少千米？(列方程解答)
<gadget id="calculator">1 / 25</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/25) + (1/15)</gadget>
<output>8/75 = around 0.106667</output>

<gadget id="calculator">4 / (8/75)</gadget>
<output>75/2 = around 37.5</output>

<result>75/2 = around 37.5</result>