1. **State the problem:** Sidney used 6241 units of electricity. The first 2400 units cost 7p each, and all units beyond 2400 cost 12p each. We need to find the total cost. 2. **Formula and rules:** Total cost = (Cost of first 2400 units) + (Cost of remaining units) 3. **Calculate cost of first 2400 units:** $$2400 \times 7 = 16800 \text{ pence}$$ 4. **Calculate remaining units:** $$6241 - 2400 = 3841 \text{ units}$$ 5. **Calculate cost of remaining units:** $$3841 \times 12 = 46092 \text{ pence}$$ 6. **Calculate total cost in pence:** $$16800 + 46092 = 62892 \text{ pence}$$ 7. **Convert pence to pounds:** Since 100 pence = 1 pound, $$\frac{62892}{100} = 628.92 \text{ pounds}$$ **Final answer:** Sidney's total electricity cost is **628.92 pounds**.