I need help with the following problem: Let us denote the water level in a dam at time $t$ by $X(t)$, where $t$ is measured in months. We will assume that, at least until the first time that the dam gets empty (i.e. $X(t) = 0$), $X$ can be modeled as a Brownian motion with drift $ \mu = +1 $ and variance $ \sigma^2 = 1 $. If the initial water level is $X_0 = 200$, find the probability that the water level reaches 210 before dropping below 100.
Any hints/pointers would be great!