Calculate the parking costs for 72 hours at Parkades P6 and P7 and determine which is cheaper.

*   **Cost for P7 (72 hours):**
    First 24 hours: R270.00 (from 8-24 hours rate)
    Remaining hours: $72 - 24 = 48$ hours.
    Number of 12-hour blocks thereafter = $\frac{48}{12} = 4$.
    Cost for remaining hours = $4 \times \text{R}135.00 = \text{R}540.00$.
    $$
    Cost P7 = R270.00 + R540.00 = R810.00
    $$
    The cost for 3 full days at P7 is $\boxed{\text{R}810.00}$.