A 400-gram bag of a kind of milk powder is priced at 31.8 yuan per bag. The merchant implements a "buy three, get one free" promotion, that is, buy 1200 grams and get 400 grams free. Aunt Wang wants to buy 2 kilograms of milk powder, how much should she pay?
一种奶粉每袋400克售价31.8元，商家实行"买三赠一"的促销活动，即购买1200克送400克，王阿姨要购买2千克奶粉，应付多少元？
<gadget id="calculator">31.8 * 3</gadget>
<output>95.4</output>

<gadget id="calculator">95.4 + 31.8</gadget>
<output>127.2</output>

<result>127.2</result>