Answer
$3\;\rm s$
Work Step by Step
We know that the induced emf is given by
$$\varepsilon=\left| \dfrac{d\Phi}{dt} \right|$$
where $ \Phi =\vec A\cdot \vec B =AB\cos90^\circ=AB$.
$$\varepsilon=\left| \dfrac{d}{dt}AB \right|$$
$$\varepsilon=A\left| \dfrac{dB}{dt} \right|$$
Hence,
$$\varepsilon=A\left| \dfrac{\Delta B}{\Delta t} \right|$$
Solving for $\Delta t$;
$$\Delta t = \dfrac{A\left| \Delta B\right|}{\varepsilon} $$
Plug the known;
$$\Delta t = \dfrac{(0.06)\left| 0-5\right|}{0.1} $$
$$\Delta t = \color{red}{\bf 3.0}\;\rm s $$