A truck drove from place A to place B to deliver goods. It took 5 hours to go there, and the speed increased to 90 km/h when it came back. As a result, it took 1 hour less than when it went to return to place A (return along the original road) ). How many kilometers per hour does this truck travel on average when delivering goods to B?
一辆货车从甲地开往乙地送货，去时一共用了5小时，回来时速度提高到90千米/时，结果比去时少用1小时就返回到甲地(沿原路返回)．这辆货车去乙地送货时平均每小时行多少千米？
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">90 * (4/5)</gadget>
<output>72</output>

<result>72</result>