There are 5 boxes of apples. Each box of apples weighs the same. If 3 kg of apples are taken from each box, the weight of the remaining apples in the 5 boxes is equal to the weight of the original 4 boxes. How many kilograms of apples are in each box?
有5箱苹果．每箱装苹果的重量相等．如果从每箱里取出3千克苹果，那么5个箱子里剩下苹果的重量相当于原来4箱苹果的重量．原来每个箱子里有多少千克苹果？
<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">5 / 1</gadget>
<output>5</output>

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<result>15</result>