Red Sun Supermarket sold 320 exercise books today, 120 more than yesterday. How many copies were sold yesterday? (solution by equation)
红太阳超市今天卖出练习本320本，比昨天多卖出120本，昨天卖出多少本？(用方程解)
<gadget id="calculator">320 - 120</gadget>
<output>200</output>

<result>200</result>