The given post-paid tariff is C₁ = R138 + 0.2343k.

Step 2 (continued): Calculate the cost for the Dlamini household using the provided post-paid tariff.
The given post-paid tariff is $C_1 = R138 + 0.2343k$.
Substitute $k = 560$ kWh:

$$C_1 = R138 + 0.2343 \times 560$$ $$C_1 = R138 + R131.198$$ $$C_1 = R269.198$$

To answer "How much more would the Dlamini household have to pay on a post-paid system, if they had an 80-amp circuit breaker?", the specific tariff structure (fixed charge and variable charge per kWh) for an 80-amp circuit breaker is required. This information is not provided in the problem statement. Without it, the difference cannot be calculated.

Question 2: Represent these two post-paid tariffs graphically to illustrate the difference this would make.
To represent "these two post-paid tariffs" graphically, both tariff equations are needed. Only one tariff ($C_1 = R138 + 0.2343k$) has been provided. The second tariff, which would correspond to the 80-amp circuit breaker, is missing. Therefore, a complete graphical representation cannot be made.