Question

x : 3 < 4. 18 : x ≤ 2

Answer 1

X:3<4/×3 =>x<12=> x={0,1,2,...,11}
18:x_<2/:18=>x_<2=>x={0,1,2}

Answer 2

1)

x/3 < 4
x < 4*3
x < 12
=> x∈(-∞, 12)
2)

18/x ≤ 2
9/x ≤ 1
9/x  - 1 ≤  0
$\frac{9-x}{x}$ ≤ 0

=> x∈(-∞, 0)∪[9,+∞)