Xiao Ming bought 3.5 kilograms of apples at the fruit shop, handed them to the salesperson for 20 yuan, and got back 4.25 yuan. How much is each kilogram of apples?
小明在水果店买了3.5千克的苹果，交给售货员20元，找回4.25元，每千克苹果多少元？
<gadget id="calculator">20 - 4.25</gadget>
<output>15.75</output>

<gadget id="calculator">15.75 / 3.5</gadget>
<output>4.5</output>

<result>4.5</result>