Aunt Wang bought 1.5 kilograms of crucian carp at the vegetable market and spent 18 yuan. If you use this money to buy silver carp, you can buy 0.5 kg more. How much is crucian carp more expensive than silver carp per kilogram?
王阿姨在菜市场买了1.5千克鲫鱼，用去18元．如果用这些钱买鲢鱼，可以多买0.5千克．每千克鲫鱼比鲢鱼贵多少元？
<gadget id="calculator">18 / 1.5</gadget>
<output>12</output>

<gadget id="calculator">1.5 + 0.5</gadget>
<output>2</output>

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

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

<result>3</result>