Mengniu pure milk in the supermarket is 45 yuan/box. If you buy 4 boxes at a time, how much is each box cheaper? (Good news: We are now conducting promotional activities, "buy 4 get 1 free. Please come)
超市里蒙牛纯牛奶45元/箱．如果一次买4箱，每箱便宜多少钱？(喜讯：现进行优惠活动，"买4送1．请您光临)
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">45 * (4/5)</gadget>
<output>36</output>

<gadget id="calculator">45 - 36</gadget>
<output>9</output>

<result>9</result>