A glass factory wants to deliver 1,000 glass cups to a shopping mall, and the two parties agree that each shipping fee will be 1 yuan. If one is broken, not only will the shipping fee not be paid, but also a compensation of 3 yuan will be paid. As a result, when the glass cup factory arrives at the destination and settles the bill, the glass cup factory will have to pay a total of 920 yuan for shipping. How many glasses were broken?
某玻璃厂要为商场运送1000个玻璃杯，双方商定每个运费为1元．如果打碎一个，这个不但不给运费，而且要赔偿3元，结果运到目的地后结算时，玻璃杯厂共得运费920元，求打碎了几个玻璃杯？
<gadget id="calculator">1_000 * 1</gadget>
<output>1_000</output>

<gadget id="calculator">1_000 - 920</gadget>
<output>80</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<result>20</result>