Answer
$$
\alpha=-1.14 \mathrm{\ rev} / \min ^{2}
$$
Work Step by Step
The angular acceleration is
$$
\alpha=\frac{\Delta \omega}{\Delta t}=\frac{0-150 \mathrm{rev} / \min }{(2.2 \mathrm{h})(60 \min / \mathrm{hh})}=-1.14 \mathrm{\ rev} / \min ^{2}
$$
