Bag A contains X kilograms of rice, and bag B contains Y kilograms of rice. If 4 kilograms are taken from bag A and put into bag B. At this time, the rice in the two bags of A and B is exactly equal, what should be the equation.
甲袋有X千克大米，乙袋有Y千克大米，如果从甲袋拿出4千克放入乙袋．这时，甲、乙两袋的大米正好相等，列成等式应是多少．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<result>8</result>