5. a) x-1.5=14.5
x=16
b) x+2=2.25
x=0.25
c) 2x+9.83=1.56×8
2x+9.83=12.48
2x=2.65
x=1.325
d) (0.1+0.2+0.3+0.4+...+0.9)×x =9
4.5x=9
x=2
e) 66.1x+7.89=14.5
66.1x=6.61
x=0.1
6. x+y=4.5
y/2=x => y=2x
x+2x=4.5
3x=4.5
x=1.5
y=3
