The equation governing the amount of current I (in amperes) after time t (in seconds) in a simple RL circuit consisting of a resistance R (in ohms), an inductance L (in henrys) and an electromotive force E (in volts) is given by

I = (E/R)[1 - e^(-(R/L))t]

If E = 12 volts, R = 10 ohms and L = 5 henrys, how long does it take to obtain a current of 0.5 ampere?