The plot given below is of the average power delivered to an LRC circuit versus frequency. The quality factor of the circuit is :

The lower cutoff frequency ($$f_1$$) is halfway between $$3.5$$ and $$4.0$$, which is $$3.75\text{ kHz}$$.

The upper cutoff frequency ($$f_2$$) is halfway between $$6.0$$ and $$6.5$$, which is $$6.25\text{ kHz}$$

$$\Delta f = f_2 - f_1 = 6.25\text{ kHz} - 3.75\text{ kHz} = 2.5\text{ kHz}$$

The maximum power occurs exactly at $$f_0 = 5\text{ kHz}$$

$$Q = \frac{f_0}{\Delta f}$$

$$Q = \frac{5\text{ kHz}}{2.5\text{ kHz}} = 2.0$$