Two coils have self-inductances L1=0.5H and L2=2.0H. Their coefficient of coupling is k=0.80. The current in the primary varies with time as I=3t2+2t (in amperes, t in seconds). The magnitude of the emf induced in the secondary at t=1s is
(a) 8.0V
(b) 4.8V
(c) 6.4V
(d) 5.6V