Aunt Li bought 8 kilograms of apples and 6 kilograms of grapes, and spent 72 yuan each on the apples and grapes. How much more expensive per kilogram of grapes than per kilogram of apples?
李阿姨买了8千克苹果和6千克葡萄，买苹果和葡萄各花了72元．每千克葡萄比每千克苹果贵多少钱？
<gadget id="calculator">72 / 6</gadget>
<output>12</output>

<gadget id="calculator">72 / 8</gadget>
<output>9</output>

<gadget id="calculator">12 - 9</gadget>
<output>3</output>

<result>3</result>