Let x be the length of the shortest board then x + 3 and 2x are the lengths of the second and third piece, respectively.
⇒ x+(x + 3) + 2x ≤ 91 and 2x ≥ (x + 3) + 5
4x ≤ 88 and x ≥ 8
⇒ x ≤ 22 and x ≥ 8
⇒ 8 ≤ x ≤ 22.
∴ The possible length of board is at least 8 cm long but not more than 22 cm long.