Answer
0.15 mV.
Work Step by Step
Use Faraday’s law.
$$|\epsilon_{av}|=|\frac{\Delta \Phi_B}{\Delta t}|=A |\frac{\Delta B}{\Delta t }| $$
$$=\pi (0.011m)^2 \frac{8.0T-0}{20s} =1.5\times10^{-4}V$$
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