Х:(450-390)=4; 39-х=49:7; 56:х=800:100; (360:6):х=4
X:(450-390)=4 39-X=49:7 56:X=800:100 (360:6):X=4 X:60=4 39-X=7 56:X=8 60:X=4 X=4*60 X=39-7 X=56:8 X=60:4 X=240 X=32 X=7 X=15