In an RL Series Circuit Connected to a Dc Source

Multiple Choice

In an RL series circuit connected to a dc source and a switch, the inductor gets 40% of its maximum current 1.8 s after the switch is closed at t = 0 s. What is the time constant of this circuit?

A) 0.80 s
B) 1.5 s
C) 2.5 s
D) 3.5 s
E) 5.5 s