Huaqiang Life Supermarket, originally 18 yuan per cup of milk tea, now has a promotional activity "buy two cups, get one free". Xiao Ming and his parents each have a cup. How much is each cup of milk tea cheaper than before?
华强生活超市，原来每杯奶茶18元，现有优惠活动"买两杯送一杯"．小明和爸爸妈妈每人一杯，现在每杯奶茶比原来便宜多少钱？
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">18 * (2/3)</gadget>
<output>12</output>

<gadget id="calculator">18 - 12</gadget>
<output>6</output>

<result>6</result>