(i) To find the length of AD, we use the angle EAD = ACD = \frac{3\pi}{10} radians. Using the sine rule in triangle ACD, we have:

\(AD = 8 \sin\left(\frac{3\pi}{10}\right)\)

Calculating this gives \(AD \approx 6.47\) cm.

(ii) To find the area of the shaded region, we calculate the area of sector ADE and subtract the area of triangle ADC.

The area of sector ADE is:

\(\frac{1}{2} \times (\text{their } AD)^2 \times \frac{\pi}{5}\)

The area of triangle ADC is:

\(\frac{1}{2} \times 8 \times (\text{their } AD) \times \sin\left(\frac{\pi}{5}\right)\)

Calculating these areas and subtracting gives the shaded area \(\approx 35.0 \text{ or } 34.9 \text{ cm}^2\).