This is the boss. No calculator — the numbers are chosen to carry in your head, the way a well-set final always is. One kettle, worked line by line, and every answer feeds the next: write them down as you go.

Everything from the chapter rides in it — the climb priced by $mc\,\Delta T$, the plateau priced by $mL$, the legs added, and the element’s kilowatts turning joules into minutes (a kilowatt is a kilojoule every second — sixty of them to the minute). 5★ under par here is the chapter crown. Put the kettle on.