a) 3x+15 < 23x<2-15
3x<-13
x<-13:3
nu avem solutie ptr x natural
b) 18 +2x ≤ 30 2x≤30-18
2x≤12
x≤12:2
x≤6
x∈{0,1,2,3,4,5,6}
c) 2(3+x ) > 123+x>12:2
3+x>6
x>6-3
x>3
x∈{3,4,6...infinit}
d) 5(2x+6) ≤ 602x+6≤60:5
2x+6≤12
2x≤12-6
2x≤6
x≤6:2
x≤3
x∈{0,1,2,3}
e) 3 ( x+ 6 ) < 18x+6<18:3
x+6<6
x<6-6
x<0
x nu are solutie in N