И c:(1200:2)=3 X+(1200-900)=1500

с:(1200:2)=3 с:600=3 с=600*3 с=1800 х+(1200-900)=1500 х+300=1500 х=1500-300 х=1200

с:(1200:2)=3 с:600=3 с=3*600 с=1800 1800:(1200:2)=1800:600=3 х+(1200-900)=1500 х+300=1500 х=1500-300 х=1200 1200+(1200-900)=1200+300=1500