1) -7+4X-8X=-9,9
-4X=-2,9
X= 2,9:4
X=0,725
2) 0,6Y-1,9Y-0,5Y=0,54
Y(0,6-1,9-0,5)=0,54
-1,8*Y=0,54
Y=0,54: -1,8
Y= - 0,3
3) X*1/8 -X*2/3+X*1/2 = -5/18
X*(1/8-2/3+1/2)=- 5/18
X*(-1/24)= - 5/18
X = 5*24/18
X=20/3
X=6 2/3
4) b* - 9 5/6+b*2 3/4+b* 1 5/12 = 1 7/27
b*( -9-5/6+2+3/4+1+5/12)=34/27
b* (-17/3) =34/27
b= - 2/9