The fruit shop buys 42 kg of apples for the first time, and 34 kg of apples for the second time. The unit price of the two times is the same, and the second time costs 20 yuan less than the first time. How much is the unit price of an apple?
水果店第一次购进42千克苹果，第二次购进34千克苹果，两次的单价一样，第二次比第一次少花20元．苹果单价是多少元？
<gadget id="calculator">42 - 34</gadget>
<output>8</output>

<gadget id="calculator">20 / 8</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>