exit time for random walk problem

Can someone help me in finding an expected time for standard linear
random walk with two exit states to reach one exit state. Say, a walk
with +1 and -1 steps (probabilities p and 1-p)  starts at the position
0 and has final states at -k and +n. What would be the expected time to
reach n?
I am going to go through stopping time theory but for now I'd like to
understand, if possible, in simple terms how such problems can be
handled.