Take a coil of 45 mH and a capacitor of 1.2 µF…

Step 1. Equal reactances. $X_L = X_C$ means $\omega L = \dfrac{1}{\omega C}$. So $\omega^2 = \dfrac{1}{LC}$.

Step 2. The angular frequency. We want $\omega$, so $\omega = \dfrac{1}{\sqrt{LC}} = \dfrac{1}{\sqrt{0.045\ \text{H} \times 1.2 \times 10^{-6}\ \text{F}}} = 4303$ rad/s.

Step 3. The frequency. $f = \dfrac{\omega}{2\pi} = \dfrac{4303\ \text{rad/s}}{2\pi} = 685$ Hz.

Step 4. The reactance. $X_L = \omega L = 4303\ \text{rad/s} \times 0.045\ \text{H} = 194\ \Omega$.