Finding the resistance of a practical inductor having its reactive power
Ther mistake you made was assuming Q meant "reactive power" - it doesn't it's the Q-factor of the coil and quite simply is \$X_L/R\$. Q-factor is something you should look up. Q is sometimes called quality factor. See this wiki page. It's embodied in an RLC resonant tuned circuit for instance by this formula: -



And, for just the inductor on its own is simply \$X_L/R\$