logistic models help!

The independent random variables $Y_{1},Y_{2},...,Y_{n},$ each $Y_{i}\in\{0,1\}$, are postulated to depend on covariates $x_{1},x_{2},...,x_{n}$ through the model,
$log\frac{\pi_{i}}{1-\pi_{i}}=\beta x_{i}$

a) Derive the equation which the maximum likelihood estimator of $\beta$ satisfies.

b) For the special case where each $x_{i} \in \{-1,0,1\}$ solve the equation in part (a). You may assume that the number of $x_{i} = j$ is $n_{j}$, $j=-1,0,1$ and that $y_{i}=1$ for $r_{j}$ of the cases where $x_{i}=j$

I'm really stuck on the part (b), can anyone either point me in the right direction or come up with a solution? Thanks!