The shopping mall launched a promotional activity, a pair of pants is 180 yuan, buy 3 and get one free. Buying 4 pairs of pants at a time, how much is each pair cheaper than the original price?
商场开展促销活动，一条裤子180元，买3条赠一条．一次买4条裤子，每条比原价便宜了多少钱？
<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">180 * (3/4)</gadget>
<output>135</output>

<gadget id="calculator">180 - 135</gadget>
<output>45</output>

<result>45</result>