Angular speed ($\omega$) is defined as Angular displacement divided by time.
For the second hand: $\omega_1 = \frac{2\pi}{60}$ rad/s; $x_1 = \omega_1 \times 60 = 2\pi$ rad.
For the minute hand: $\omega_2 = \frac{2\pi}{3600}$ rad/s; $x_2 = \omega_2 \times 60 = \frac{2\pi}{60}$ rad.
For the hour hand:
$\omega_3 = \frac{2\pi}{3600 \times 12}$ rad/s.
$x_3 = \omega_3 \times 60 = \frac{2\pi}{720}$ rad.
Consequently, $\frac{\omega_1}{x_1} = \frac{\omega_2}{x_2} = \frac{\omega_3}{x_3} = \frac{1}{60} = k$.