This is the boss. No calculator — the values are chosen to fit in your head. One circuit board: a battery, two resistors in series, and a clock on the wall. Every answer feeds the next: the total resistance, then the current, then the power, then the energy it spends before the bell. Write each line down as you go — one early slip travels all the way down the board.

The energy line is measured the friendly way, in watt-hours: a watt-hour is what one watt spends in one hour, so it is watts times hours and you are done — no joules, no ×3600, no mercy needed. 5★ under par here is the chapter crown. You've got this.