Given inequality

⇒

Multiplying the inequality by 2.

⇒ 14 ≤ 3x + 11 ≤ 22

⇒ 14 – 11 ≤ 3x + 11 – 11 ≤ 22 – 11

⇒ 3 ≤ 3x ≤ 11

∴ all real numbers x greater than or equal to -4 but less than or equal to 2 are solution of given equality.

x ∈ [1, 11/3]