finding optimal solution $w$ and classification accuracy
The best that we can do is to classify $5$ points correctly and sacrifice one point.

We want to classify $-1,0,1$ as negative and $-3,-2$ as positivie.  (we have to sacrifice $3$).

The boundary with maximum margin would be in the middle of $-2$ and $-1$. That is $-\frac32$.

$$sign(-(2x+3))=sign(-2x-3).$$