Flour is 0.92 yuan per kilogram, and rice is 0.80 yuan per kilogram. If you buy 15 grams of flour and 15 grams of rice each, and pay 30 yuan, how much should you get back?
面粉每千克0.92元，大米每千克0.80元，买面粉和大米各15克，付款30元，应找回多少钱？
<gadget id="calculator">0.92 * 15</gadget>
<output>13.8</output>

<gadget id="calculator">0.8 * 15</gadget>
<output>12</output>

<gadget id="calculator">13.8 + 12</gadget>
<output>25.8</output>

<gadget id="calculator">30 - 25.8</gadget>
<output>4.2</output>

<result>4.2</result>