12. a) 3x≥27 /:3 x≥9 x={9, 10, 11, 12, ...}
b) -5x>50 /:5 -x>50 /×(-1) x<-50 x={-51, -52, -53, ...}
c) 14≥7x /:7 2≥x x={2, 1, 0, -1, ...}
d) -2x<-24 /×(-1) 2x>24 /:2 x>12 x={13, 14, 15, ...}
e) (x-3):(-3)≤9 /×(-3) x-3≤-27 /+3 x≤-24 x={-24, -25, ...}
f) 4(1-x)>-48 /:4 1-x>-12 /-1 -x>-13 /×(-1) x<13 x={12, 11, ...}