600×20%-20%x+10%x÷600=400×10%-10%x+20%x
120-20%x+10%x÷600=40-10%x+20%x
120-10%x÷600=40+10%x
-20%x÷600=40-120
-20%x÷600=-80
-20%x=-80×600
20%x=48000
x=48000÷20%
x=240000