The original is $P = VI$ (read aloud: P equals V I) — the push times the flow is the rate of spending energy, measured in watts. Feed it Ohm's law and it changes clothes: substitute $V = IR$ and you get $P = I^2R$ (I-squared R); substitute $I = \dfrac{V}{R}$ instead and you get $P = \dfrac{V^2}{R}$ (V-squared over R). Same power, same watts, three outfits.

The exam skill is matching the face to the GIVENS: handed $V$ and $I$, use $VI$; handed $I$ and $R$, use $I^2R$; handed $V$ and $R$, use $\dfrac{V^2}{R}$. No algebra detour, no wasted minute — the right face goes straight to the number.