porter moved 500 porcelain bowls from the wholesale department to the store. The owner stipulated that the shipping fee was 30 cents for a good porcelain bowl, and 9 cents for a broken porcelain bowl. As a result, he received a shipping fee of 136.80 yuan. Then how many porcelain bowls were broken by the porter during transportation.
一名搬运工从批发部搬运500只瓷碗到商店，货主规定：运到一只完好的瓷碗得运费3角，打破一只瓷碗赔9角，结果他领到运费136.80元．则在运输中搬运工打破了多少只瓷碗．
<gadget id="calculator">0.3 * 500</gadget>
<output>150</output>

<gadget id="calculator">150 - 136.8</gadget>
<output>13.2</output>

<gadget id="calculator">0.3 + 0.9</gadget>
<output>1.2</output>

<gadget id="calculator">13.2 / 1.2</gadget>
<output>11</output>

<result>11</result>