If you buy 3 notebooks, 5 pencils, and 1 ruler, the total cost is 6.10 yuan; if you buy 4 notebooks, 7 pencils, and 1 ruler, the total cost is 7.92 yuan. So how much is the total cost of buying a notebook, a pencil, and a ruler?
若购买笔记本3本、铅笔5支、格尺1个，共需6.10元；若购买笔记本4本、铅笔7支、格尺1个，共需7.92元．那么购买笔记本、铅笔、格尺各一件一共需要多少元．
<gadget id="calculator">6.1 * 3</gadget>
<output>18.3</output>

<gadget id="calculator">7.92 * 2</gadget>
<output>15.84</output>

<gadget id="calculator">18.3 - 15.84</gadget>
<output>2.46</output>

<result>2.46</result>