Random Walk

You are initially located at origin in the $x$-axis. You start a random walk with equal probability of moving left or right one step at a time. Let $a,b$ be natural numbers. (As a warm-up, find the expression for the probability that you will reach point $a$ before reaching point $-b$.)
What is the expected number of steps until you first reach either $a$ or $-b$? Calculate this expected number for $a=3$ and $b=4$.