3х + (х+2) = 2*(3х+12)
И второе)) 25,8z-4,3*(6z+300) = 25,8z

1)3х+х+2=6х+24
3х+х+2-6х-24=0
-2х-22=0
-2х=22
х=-11
2)25,8z-25,8z-1290=25,8z
25,8z-25,8z-1290-25,8z=0
-1290-25,8z=0
-25,8z=1290
z=1290/(-25,8)=-50