In the supermarket, the original price of a box of toothpaste is 8.7 yuan, and now the supermarket is discounting, buy two boxes and get a 15% discount, how much money can mother save by buying four boxes now?
超市中，一盒牙膏原价8.7元，现在超市开始打折，买两盒打八五折，妈妈现在买四盒可以省多少钱？
<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">1 - (17/20)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">8.7 * (3/20) * 4</gadget>
<output>5.22</output>

<result>5.22</result>