Uncle Wang bought 4 kilograms of flour and 20 kilograms of rice in January for a total of 48 yuan; in February he bought 5 kilograms of flour and 40 kilograms of rice for a total of 87 yuan. How much is flour per kilogram.
王大伯1月份买了4千克面粉和20千克大米，一共用去48元；2月份买了5千克面粉和40千克大米，一共用去87元．面粉每千克多少元．
<gadget id="calculator">96 - 87</gadget>
<output>9</output>

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

<result>3</result>