∵0.9x-y=180
0.8x-y=-240
∴9x-10y=1800 ①
8x-10y=-2400 ②
①-②：x=1800-(-2400)
∴x=4200
将x=4200代入①得：9×4200-10y=1800
y=3600
因此,x=4200
y=3600
这方程怎么解答的啊,一道而已,0.9x-y=1800.8x-y=-240解得x=4200,y=3600
∵0.9x-y=180
0.8x-y=-240
∴9x-10y=1800 ①
8x-10y=-2400 ②
①-②：x=1800-(-2400)
∴x=4200
将x=4200代入①得：9×4200-10y=1800
y=3600
因此,x=4200
y=3600