68:(х+15)=4
68=4(х+15)
68=4х+60
4х=68-60
4х=8
х=8:4
х=2
__________
68:(2+15)=4
68:17=4
4=4
12:х=20-16
12=(20-16)*х
12=20х-16х
12=4х
х=12:4
х=3
______________
12:3=20-16
4=4
(340+х)-160=840
340+х-160=840
х+180=840
х=840-180
х=660
_____________
(340+660)-160=840
1000-160=840
840=840
(х-300)+260=750
х-300+260=750
х=750+300-260
х=790
_____________
(790-300)+260=750
490+260=750
750=750