0.5x=0.75(1000-x)
2x=3(1000-x)
2x=3000-3x
2x+3x=3000
5x=3000
x=6002x=3(1000-x)2x=3000-3x2x+3x=30005x=3000x=600 哪来的2x先两边乘以4