Rice is 8.8 yuan per kilogram, and flour is 9.2 yuan per kilogram. If you buy 15 kilograms of flour and 15 kilograms of rice each, and pay 300 yuan, how much should you get back?
大米每千克8.8元，面粉每千克9.2元．买面粉和大米各15千克，付出300元钱，应找回多少元？
<gadget id="calculator">18 * 15</gadget>
<output>270</output>

<gadget id="calculator">300 - 270</gadget>
<output>30</output>

<result>30</result>