200x+170(70-x)+160(40-x)+150[30-(40-x)]解的步骤

200x+170(70-x)+160(40-x)+150[30-(40-x)]
=200x+11900-170x+6400-160x+150(30-40+x)
=200x+11900-170x+6400-160x+150(-10+x)
=200x+11900-170x+6400-160x-1500+150x
=(200x-170x-160x+150x)+(11900+6400-1500)
=20X+16800