Calculate the total amount payable for water including VAT and sewage, and the amount spent on electricity.

Sewage is 30% of the water cost (excluding VAT).

$$\text{Sewage cost} = 30\% \times \text{Water cost (excluding VAT)}$$ $$\text{Sewage cost} = 0.30 \times \text{R}94.20$$ $$\text{Sewage cost} = \text{R}28.26$$

This is the sum of the water cost (excluding VAT) and the sewage cost.

$$\text{Amount before VAT} = \text{Water cost (excluding VAT)} + \text{Sewage cost}$$ $$\text{Amount before VAT} = \text{R}94.20 + \text{R}28.26$$ $$\text{Amount before VAT} = \text{R}122.46$$

VAT is 15% of the amount before VAT.

$$\text{VAT amount} = 15\% \times \text{Amount before VAT}$$ $$\text{VAT amount} = 0.15 \times \text{R}122.46$$ $$\text{VAT amount} = \text{R}18.369$$

Rounding to two decimal places:

$$\text{VAT amount} = \text{R}18.37$$

$$\text{Total amount payable} = \text{Amount before VAT} + \text{VAT amount}$$ $$\text{Total amount payable} = \text{R}122.46 + \text{R}18.37$$ $$\text{Total amount payable} = \text{R}140.83$$ $$\boxed{\text{R}140.83}$$

From the Monthly Budget in Question 1, Mrs Ncube's electricity and water expense was R1 100.
We need to find the electricity cost for September 2020. We have calculated the total water and sewage cost for September 2025 (R140.83). Assuming the water cost is similar for 2020, we can subtract the water cost from the combined electricity and water budget.
However, the question asks for electricity spent during the month of September 2020. The budget provided in Question 1 is a monthly budget without a specific year, but the water calculation is for September 2025. It's best to use the budget value directly for electricity and water, and then subtract the water cost for 2020 if it was provided. Since it's not, and the question asks for electricity based on the monthly budget in Question 1 and your Water tariffs in Question 2, it implies using the calculated water cost from 2.2.2.

Let's assume the R1 100 for "Electricity and water" from the budget in Question 1 applies to September 2020, and the calculated water cost (R140.83) is also applicable.

$$\text{Electricity cost} = \text{Budgeted Electricity and water} - \text{Total amount payable for water}$$ $$\text{Electricity cost} = \text{R}1\,100 - \text{R}140.83$$ $$\text{Electricity cost} = \text{R}959.17$$ $$\boxed{\text{R}959.17}$$