Uncle Wang wants to buy 30 boxes of milk, 24 boxes in each box. A supermarket is 2.5 yuan per box, 58 yuan per box. Supermarket B buys 1 box and gets 2 boxes free, each box is 2.6 yuan, and each box is 62 yuan. Which supermarket is cheaper? How much cheaper?
王叔叔要买30盒牛奶，每箱24盒．A超市每盒2.5元，每箱58元．B超市买一箱送2盒，每盒2.6元，每箱62元．哪家超市便宜？便宜多少钱？
<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<gadget id="calculator">6 * 2.5</gadget>
<output>15</output>

<gadget id="calculator">58 + 15</gadget>
<output>73</output>

<gadget id="calculator">30 - 24 - 2</gadget>
<output>4</output>

<gadget id="calculator">4 * 2.6</gadget>
<output>10.4</output>

<gadget id="calculator">62 + 10.4</gadget>
<output>72.4</output>

<gadget id="calculator">73 - 72.4</gadget>
<output>0.6</output>

<result>0.6</result>