The shopping mall launched a promotional activity, each bottle of Golden Dragon Oil is 80 yuan, buy 3 bottles and get a free bottle, buy 3 bottles at a time, how much is each bottle cheaper?
商场开展促销活动，每瓶金龙油80元，买3瓶赠送一瓶，一次买三瓶，每瓶便宜多少钱？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">80 * (3/4)</gadget>
<output>60</output>

<gadget id="calculator">80 - 60</gadget>
<output>20</output>

<result>20</result>