400:(230-190)•8=, 600:(780-680)•9=, 36000:1000:4

400:(230-190)*8=400:40*8=10*8=80 600:(780-680)*9=600:100*9=60*9=540 36000:1000:4=36:4=9

1)400:(230-190)•8=801)230-190=402)400:40=103)10•8=802)600:(780-680)•9=541)780-680=1002)600:100=63)6•9=543)36000:1000:4=91)36000:1000=362)36:4=9