(x-40)(200+(50-x)×100)=3500
(x-40)(5200-100x)=3500
-100x²+9200x-208000=3500
x²-92x+2115=0
(x-47)(x-45)=0
x-47=0 x=47
或 x-45=0 x=45
(x-40)(200+(50-x)×100)=3500
(x-40)(5200-100x)=3500
-100x²+9200x-208000=3500
x²-92x+2115=0
(x-47)(x-45)=0
x-47=0 x=47
或 x-45=0 x=45