Chapter 23 - Magnetic Flux and Faraday's Law of Induction - Problems and Conceptual Exercises - Page 835: 101

$(B)\ 0.11s$

We know that $\epsilon=N|\frac{(B_2-B_1)l^2}{\Delta t}|$ This can be rearranged as: $\Delta t=N|\frac{(B_2-B_1)l^2}{\epsilon}|$ We plug in the known values to obtain: $\Delta=(4)|\frac{1.9\times 10^{-5}-1.2\times 10^{-5}(0.75)^2}{1.4\times 10^{-4}}|=0.11s$