Mix the first-grade and second-grade sugar together, and buy an average of 7 yuan per kilogram. It is known that the first-grade sugar is 4 kilograms, and the average is 8 yuan per kilogram, and the second-grade sugar is 2 kilograms. How much is it per kilogram?
把一级和二级糖混在一起，平均每千克买7元，已知一级糖有4千克，平均每千克8元，二级糖有2千克，每千克多少元？
<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">6 * 7</gadget>
<output>42</output>

<gadget id="calculator">4 * 8</gadget>
<output>32</output>

<gadget id="calculator">42 - 32</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<result>5</result>