The fruit supermarket buys back a batch of apples at a price of 2.8 yuan per kilogram. After selection, this batch of apples is divided into two grades, A and B. The weight ratio of A and B is 5:3, and the price of B can only be 2.5 yuan. If the supermarket wants to obtain a 25% profit, how much should the first-class apples be sold per kilogram?
水果超市以每千克2.8元的价格购回一批苹果，经过挑选，把这批苹果分成了甲、乙两等，甲、乙两等的重量比是5：3，乙等只能以2.5元的价格出售，超市要想获得25%的利润，甲等苹果每千克应卖多少元？
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">8 * 2.8 * (5/4)</gadget>
<output>28</output>

<gadget id="calculator">2.5 * 3</gadget>
<output>7.5</output>

<gadget id="calculator">28 - 7.5</gadget>
<output>20.5</output>

<gadget id="calculator">20.5 / 5</gadget>
<output>4.1</output>

<result>4.1</result>