1. **State the problem:** We are given the sum of the interior angles of a polygon as 1620° and need to find the number of sides of the polygon. 2. **Formula:** The sum of the interior angles $S$ of a polygon with $n$ sides is given by: $$S = 180(n - 2)$$ 3. **Apply the formula:** Substitute $S = 1620$ into the formula: $$1620 = 180(n - 2)$$ 4. **Solve for $n$:** $$\frac{1620}{180} = \frac{180(n - 2)}{180}$$ $$9 = n - 2$$ 5. **Find $n$:** $$n = 9 + 2 = 11$$ 6. **Conclusion:** The polygon has 11 sides.