500×0.9-（X-500)×0.8=554

500×0.9-（X-500)×0.8=554
450-(X-500)×0.8=554
（X-500)×0.8=-96
X-500=-120
X=500-120
X=380错的吧500×0.9-（X-500)×0.8=554450-(X-500)×0.8=554（X-500)×0.8=-104X-500=-130X=500-130X=370是630,但不知怎么算？那肯定是你题目出错了