Complex sentence: In one, prefixed values cannot be multiplied or divided together, and they have to be converted into non-prefixed standard form for such calculations, hence 5 mV × 5 mA ≠ 25 mW.
Split into simpler sentences: In one, prefixed values cannot be multiplied or divided together, so they must be converted into non-prefixed standard form for such calculations. Hence 5 mV × 5 mA ≠ 25 mW.