The fertilizer factory produces 54 tons of fertilizer in 9 hours. If this is the case, it needs to produce 72 tons more. How many hours will it take in total?
化肥厂9小时生产化肥54吨，照这样，要多生产72吨，一共需要多少小时？
<gadget id="calculator">54 / 9</gadget>
<output>6</output>

<gadget id="calculator">72 / 6</gadget>
<output>12</output>

<gadget id="calculator">12 + 9</gadget>
<output>21</output>

<result>21</result>