Perimeter of a square side 9 cm.

**The reasoning** A square has **four equal sides**. That's the key property you must remember. If one side = 9 cm, then all four sides = 9 cm each. **Perimeter** means the total distance around the shape — you add up all the sides. So: Perimeter = 9 + 9 + 9 + 9 = **36 cm** Or use the formula: **Perimeter of square = 4 × side = 4 × 9 = 36 cm** --- **Why the wrong options tempt you** - **18 cm (A):** You only added two sides (9 + 9). A square has *four* sides, not two! - **27 cm (B):** You multiplied by 3 instead of 4. Maybe confusion with triangles? Squares have 4 sides. - **81 cm (D):** You calculated the **area** (9 × 9 = 81 cm²), not the perimeter. Area uses multiplication of length × width; perimeter uses addition of all sides. --- **Quick takeaway** Perimeter = distance *around* = **add all sides**. For a square with side *s*: **P = 4s**. Never confuse it with area (s²)!