This is the boss. No calculator — today $\sqrt{3} = 1.73$, the number every electrician keeps in their head, and the values are chosen to fit in yours. One feeder, one long problem, and every answer feeds the next: the real power on the line, then the month's kilowatt-hours, then the dollars at 10 ¢, then the capacitor bank that would trim the reactive leg away. Write each line down as you go — one early slip rolls all the way to the invoice.

One gift, already in the numbers: at a power factor of 0.80 the triangle is the 3-4-5, so $\tan\varphi = \dfrac{0.6}{0.8} = 0.75$ exactly. The last line needs no trigonometry at all, only that fraction.

Everything in the chapter rides on this one feeder — the √3, the meter, the tariff and the triangle. 5★ under par here is the chapter crown. Clock in.