1. The problem states the total cost $c$ in pence for $n$ units of electricity is given by the formula: $$c = 17n + 12$$ where $c$ is the total cost and $n$ is the number of units. 2. This is a linear equation representing a straight line where: - The slope (rate per unit) is 17 pence per unit. - The fixed cost (standing charge) is 12 pence. 3. To find the total cost for any number of units, substitute the value of $n$ into the formula and calculate $c$. 4. For example, if $n=5$ units: $$c = 17 \times 5 + 12 = 85 + 12 = 97$$ So, the total cost is 97 pence. 5. This formula can be graphed as a line with intercept 12 on the $c$-axis and slope 17, showing how cost increases with units used. Final answer: The total cost $c$ for $n$ units is given by $$c = 17n + 12$$.