The area of a parallelogram can be calculated using the formula:
\[ \text{Area} = \text{base} \times \text{height} \]
Given that the area is 216.24 cm² and the height is 15.9 cm, we can rearrange the formula to solve for the base:
\[ \text{base} = \frac{\text{Area}}{\text{height}} \]
Substituting the known values into the equation:
\[ \text{base} = \frac{216.24 , \text{cm}^2}{15.9 , \text{cm}} \]
Now, we calculate the base:
\[ \text{base} = \frac{216.24}{15.9} \approx 13.6 , \text{cm} \]
Therefore, the length of the base of the parallelogram is approximately:
\[ \boxed{13.6} , \text{cm} \]