Answer
$4\ rad/s$
Work Step by Step
From the kinematic equations, time taken by the toast to fall is:
$t =\sqrt \frac{2s}{g}$
$t =\sqrt \frac{2\times 0.76\ m}{9.8\ m/s^2}$
$t=0.394\ s$
For minimum angular speed, the toast rotates at $\frac{1}{4}$ of a revolution.
The formula for angular speed is $\omega = \frac{\Delta\theta(\ rev)}{\Delta T(sec)}$
Therefore;
$\omega_{min} =\frac{0.25\ rev}{0.394\ s}$
Since $1\ rev = 2\pi rad$;
$\omega_{min} =\frac{0.25 \times 2\pi\ rad}{0.394\ s} =3.986= 4\ rad/s$
