Given inequality

⇒

Multiplying the inequality by -2.

⇒ 14 ≥ 7x ≥ -28

⇒ -28 ≤ 7x ≤ 14

Dividing the inequality by 7

⇒ -4 ≤ x ≤ 2

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

x ∈ [-4, 2]