10×x=8×25 x:20=4800:80
10×x=200 x:20=60
x=200:10 x=20×60
x=20 x=1200
(x-380)×50=2000 (x+8):70=4
x-380=2000:50 x+8=4×70
x-380=40 x+8=280
x=380+40 x=280-8
x=420 x=272
640:(25-x)=40 2700:(x-12)=90
25-x=640:40 x-12=2700:90
25-x=16 x-12=30
x=25-16 x=30+12
x=9 x=42