This is the boss. No calculator — every value on this board has been chosen to divide cleanly in your head. One circuit, one long problem, and every answer feeds the next: reduce the parallel pair, add the series resistor, find the supply current, find the drop across the series resistor, then the heat it makes. Write each line down as you go, because one early slip rolls all the way to the bottom.

Note what the last line actually asks for. It does not want another number — it wants a decision, the way a real check does: is the part in your hand rated for the job. The arithmetic is only there to earn you the right to make it, and the only line you may compare with a wattage rating is the line that is measured in watts.

Everything in the chapter rides in this one board. 5★ under par here is the chapter crown. Clock in.