Mom and Aunt Wang spent the same amount of money to buy a basket of apples together. Mom got 8 kilograms, and Aunt Wang only got 5 kilograms. In the end, mom paid Aunt Wang 4.2 yuan. How much is the apple per kilogram?
妈妈和王阿姨拿出同样多的钱合买一筐苹果，妈妈分到8千克，王阿姨只分到5千克，结果妈妈又付给王阿姨4.2元，苹果每千克多少元？
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">13 / 2</gadget>
<output>13/2 = around 6.5</output>

<gadget id="calculator">8 - (13/2)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">4.2 / (3/2)</gadget>
<output>2.8</output>

<result>2.8</result>