3/2q≤9/2q-18

3/2 ≤ (9/2)q-18      multiply throgh by 2

3 ≤ 9q - 36     add 36 to both sides

39 ≤ 9q      divide both sides by 9

39/9 ≤ q

13/3 ≤ q      is the same as   q  ≥ 13/3