И c:(1200:2)=3
X+(1200-900)=1500

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

с:(1200:2)=3с:600=3с=3*600с=18001800:(1200:2)=1800:600=3х+(1200-900)=1500х+300=1500х=1500-300х=12001200+(1200-900)=1200+300=1500