plot of a function of time

a matlab question..

A resistor, R = 4 ohms, and an inductor, L = 1.3H, are connected in a circuit to a voltage source as shown in Figure (a) (RL circuit). When the voltage source applies a rectangular voltage pulse with an amplitude of V = 12V and a duration of 0.5 s, the current i(t) in the circuit as a function of time is given by: http://img255.imageshack.us/img255/5031/untitledva1.png

make a plot of the current as a function of time for 0 <= t <= 2 s.

my question is, which equation do I use, there appears to be two?

thanks for any help.