A 250-gram bag of high-calcium milk, the original price is 1.8 yuan per bag, now the promotion "buy 6 get 1 free", my mother bought 28 bags of this milk. How much does she pay?
一种250克一袋的高钙牛奶，原价每袋1.8元，现在促销"买6送1"，妈妈买了这种牛奶28袋．她应付多少元？
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<gadget id="calculator">6 / 7</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">28 * 1.8 * (6/7)</gadget>
<output>43.2</output>

<result>43.2</result>