A large barrel can hold 4.5 kilograms of oil, and a small barrel can hold 2.5 kilograms of oil. If 40 large barrels are filled with small barrels, how many small barrels are needed?
一只大桶能装4.5千克油，一只小桶能装2.5千克油，40只大桶装的油如果用小桶来装，需要多少只小桶？
<gadget id="calculator">40 / 2.5</gadget>
<output>16</output>

<gadget id="calculator">4.5 * 16</gadget>
<output>72</output>

<result>72</result>