x-y=8, (1)
y-z=9 (2)
x+y=174, (3)
(1)+(3)=> x-y+x+y=8+174 => 2x=281 => x=281/2= 91
(30-(1)=> x+y-x+y=174-8 => 2y=166 => y=166/2=83
y-z=9 ⇒ 83-z=9 ⇒ z=83-9=74
x=91
y=83
z=74
2.
320:{[340-(120-4*x)]:10+6}=10
320={[340-(120-4*x)]:10+6}*10
32=340-(120-4*x)]:10+6
32-6=[340-(120-4*x)]:10
26=[340-(120-4*x)]:10
260=340-(120-4*x)
(120-4*x)=340-260
120-4*x=80
120-80=4*x
40=4*x
x=40:4
x=10
3.A+B+C= 2050
A-B=75 => B=A-75
C:A=5 rest 25 ⇒C=5A+25
A+(A-75)+(5A+25)=2050
7A-50=2050
7A=2100
A=300
B=300-75=225
C=300*5+25=1525