During the "June 1st" period, Xiaoli went to Xinhua Bookstore to buy a set of science and technology books. The original price was 42 yuan, and now they are on sale at a 15% discount.
"六一"期间，小丽到新华书店买了一套科技读物，原价42元，现在打八五折销售，此时买这套书便宜多少元？
<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">42 * (3/20)</gadget>
<output>63/10 = around 6.3</output>

<result>63/10 = around 6.3</result>