72-х=18*3
72-х=64
х=72-64
х=8
72-8=18*3
64=64
х:8=130+270
х:8=400
х=400*8
х=3200
3200:8=130+270
400=400
х-290=470+230
х-290=700
х=700+290
х=990
990-290=470+230
700=700
х+320=90*8
х+320=720
х=720-320
х=400
400+320=90*8
400=400
15*х=630:7
15*х=90
х=90:15
=-----------------
х=6
15*6=630:7
90=90
400:х=1000:10
400:х=100
х=400:100
х=4
400:4=1000:10
100=100
х+320=90*8